Corsair HX650w 650W ATX PSU Page: 1

 Corsair HX650w's good to be back in the reviewing seat again. After almost 3 months of coding the new Overclock3D website (which I hope you like), the itch for testing PSU's to within an inch of destruction needed to be scratched. And what a better place to start than Corsair's HX650w...that, *ahem* has been sitting at the OC3D offices since October (sorry!).

Truth be told, I actually started this review a while ago. So these random mumblings are really just a filler for the original text which told you all about how the HX650W is the successor to the original HX620W, how it was released pretty much on its 3rd birthday, and how the original unit achieved an almost iconic status among the enthusiast communities who recommended it for its stability, silent operation and cool modular cables.

But, let's get back on task. The recently announced HX650W is what we're talking about here, and although the unit clearly sports an extra 30w of power over it's predecessor, this isn't what it's all about. So what better place to start than the specifications pulled straight from Corsair's website to try and clear a few things up:

- Guaranteed to sustain its full rated wattage at an ambient temperature of 50°C - Up to 85% energy-efficiency under real-world load conditions*
- Single +12V rail design providing up to 52A
- Multi-GPU ready
- Active Power Factor Correction (PFC) with PF value of 0.99
- Supports ATX12V 2.2 and EPS12V 2.91 standards. Backwards compatible with ATX12V 2.01
- Auto switching circuitry for universal AC input from 90-264V
- Over Current/Voltage/Power Protection, Under Voltage Protection and Short Circuit Protection provide complete component safety
- Dimensions: 150mm(W) x 86mm(H) x 150mm(L)
- MTBF: 100,000 hours - Safety Approvals: UL, CUL, CE, CB, FCC Class B, TÜV, CCC, C-tick

Looking through the list, a large number of the specifications can be matched to those of the HX620W. For example, both PSU's are exactly the same size. Both have the same list of safety features including OCP, OVP and OPP, and both are guaranteed to deliver their full output at a toasty 50°C. But, similarities are not what we're interested in here, so what about the improvements?

Well firstly, there's 80PLUS Bronze certified efficiency up to 85%. This is 5% higher than the rated efficiency of the HX620W and certainly brings the unit up to more modern standards. I do say that between gritted teeth though, as it still falls short of the ~90% efficiency achieved by the HX750W and HX850W units which i was hoping the HX650W would mimic. Then of course there is the single +12v rail rated at 52A. But yet again, don't get too excited as the HX620W was capable of delivering 50A on a single +12v rail, despite having 3x 18A rails on paper.  

Corsair HX650w Rail Layout
DC Output +3.3V +5V +12V1 +12V2 +12V3 +12V4 +12V5 +12V6 -12V +5VSB
24A 30A 52A - - - - - 0.8A 3A
Max Power 170W 624W 9.6W 15W

The +3.3v and +5v rails also mimic those of the HX620W which isn't exactly surprising as I doubt Corsair wanted to make the HX650W any less powerful in this area than it's predecessor. But never less it's worthy of note that the combined 170W output of these two rails bests the comparative 150w output of the HX750W and HX850W.

So we're off to a bit of a slow start with only a few minor differences apparent on paper between the units new and old. Maybe the dissection over the next few pages will reveal more... 

Corsair HX650w 650W ATX PSU Page: 2

 Corsair HX650w

Just like its bigger brothers, the HX650W is packaged inside a light blue and black box with an up-close picture of the PSU modular connectors dominating a large portion of the box. At the top-left is badge depicting Corsair's excellent 7 year warranty, but aside from this there are no other certification or specification stickers (such as 80PLUS / SLI /Crossfire) to be seen anywhere. Truth be told, the box design doesn't exactly jump off the shelves at you, but then again who really goes into a PC shop to buy their hardware these days anyway?

HX650w Box Front HX650w Box Back

HX650w Box Side HX650w Box Side

Flipping the box over we can see that Corsair have printed a basic specification list in just about every European language. At the top of the list is a selection of thumbnail images showing off the modular cables, fan grill and capacitors. But the sides of the box is where the information junkies will get their fix...

Over on the left side we have two line graphs that represent the HX650W's efficiency at various load levels and also the noise output of the unit as the wattage is increased. Going by the graphs it would seem that the HX650W performs its absolute best at around 325-400W. Also included on this side of the packaging is the DC Output Rating chart which we discussed on the previous page.

At the right side of the box is some more thumbnail images, only this time depicting how many connectors of each type are included in the unit. This is especially handy if you do happen to purchase the PSU from a store and need to know in advance whether it has enough connectors to power all the hard disks in your 20TB media server! 


As per usual Corsair's internal packaging is second to none. Two large styrofoam slabs completely encase the entire PSU, and a clear plastic bag prevents anything from rubbing at the PSU's paintwork during transit. As I've said many a time before: "It would take one seriously incompetent or clumsy courier to damage this PSU".... either that or City Link.

The modular cables are provided in their own separate velcro sealed black canvas bag, and all of the usual gubbins to get you up and running (manual, screws, power cord, cable ties) are tucked neatly at the side of the box.


Aside from the change in sticker colour from red to blue, there is very little to differentiate the HX650w from the HX620w at first glance. The fan size and positioning (slightly to one side) is all identical and the only minor difference is the Corsair logo badge affixed to the center of the fan grill, rather than simply being a sticker attached to the fan hub. Once again, Corsair have gone for a textured powdercoat finish for maximum durability.


The specifications sticker is hidden away at the top of the unit and therefore shouldn't be visible inside a windowed PC case (unless of course your case mounts the PSU on its side). For most of us this probably wont affect the purchasing decision either way, but it's always good to see a manufacturer taking the appearance of their PSU into consideration.

At the rear of the unit, everything is pretty much standard with a normal 'kettle' style mains lead, power switch and honeycomb mesh exhaust grill. One could comment that the area above the switch and power socket could have been put to better use with more meshing, but considering that all HX units have followed this design and not suffered from poor airflow, I'm probably just nitpicking.

Corsair HX650w 650W ATX PSU Page: 3

Corsair HX650w

Around the front of the unit we have the modular cable connector area which consists of five propitiatory flat style connectors and two 6-Pin PCI-E connectors. As you will have probably guessed, the flat style connectors are used for the SATA and Molex modular cables, whereas the PCI-E style connectors are used for....the PCI-E graphics card cables. This is exactly the same layout as the HX620W (but different to the HX750W/HX850W), and most likely indicates that Corsair decided to use the same OEM for the HX650w as they did for the HX620w (Seasonic), rather than finishing off their new HX range with just CWT built units.


In addition to the modular connectors, two essential cables - the EPS-12v and ATX are hard wired into the unit. This not only ensures that critical system components get a good; clean supply of power direct from the PSU, but also avoids potential situations where an ill-fitted modular cable could cause system instability or even kill components.

Corsair HX850W Connectors
 ATX Connector Native 1x 20+4 Pin
 EPS-12v / P4-12v Connector(s) Native 1x 4+4 Pin
 Molex Connectors Modular 8x
 Floppy Disk Connectors Modular 2x
 SATA Connectors Modular 9x
 PCI-E Connectors Modular 2x 6+2 Pin


A total of 7 modular cables has been included by Corsair, meaning that every cable can be plugged into the unit at the same time. Although it's sometimes nice to have a few spares of each modular cable type, It's highly unlikely that the average user buying a 650W PSU will be using more than eight molex or nine SATA connectors in their system.

While on the subject of modular cables, its good to see that Corsair have stuck with the black ribbon style wires rather than going down the sleeving route. Personally I love the look of these cables as they are easily camoflaged inside a case with black internals and look so much more professional than wires wearing a pear of stockings! Of course, the only downside to them is that they only bend easily in two directions (much like a PATA cable) meaning that they are slightly less flexible than normal bunched cables which can bend in any direction.


Going in for a closer look at the ATX 24-Pin, EPS 8-Pin and PCI-E 8-Pin connectors we can see that Corsair have retained compatibility with older/lower range motherboards and graphics cards by allowing certain parts of the connectors to be snapped off  in order to support 20-Pin, 4-Pin and 6-Pin standards respectively. This feature has been dropped from a lot of manufacturers PSU's, so it's good to see that Corsair realise the importance of keeping this feature on the lower wattage models.

The Guts

With the HX620W literally rocketing Corsair's PSU venture into success, its understandable that they wouldn't want to make too many changes to the HX650W. This is certainly visible when you lift the lid off the HX650W, as the general layout at least, is pretty much a direct clone of its predecessor.



Everything inside the unit is well arranged with all cables on the output side tidily bunched together. A black PCB replaces the original green PCB of the HX620W maybe hinting that Corsair have got a little more specific with their requirements from Seasonic this time around. The main transformer for the +12v, +5v and +3.3v rails inside the unit is positioned right up against the modular backplane with a smaller transformer solely responsible for the 5vSB (stand-by voltage) rail over on the right.


Sitting slap bang in the middle of the unit is a tasty Japanese manufactured Nippon Chemicon capacitor that performs a large part of the input filtering for the primary side of the unit. The markings on the capacitor suggest that it is rated up to 400v at 105°C with a respectable 560 micro Farads (uF) capacitance. Over on the secondary (low voltage) side are a collection of various spec capacitors, once again all manufactured by Nippon Chemicon.


An EMI filtering circuit has been installed just behind the AC inlet on a rather tidy PCB. This should help to keep any internally generated noise from the MOSFET's and other components contained within the device, while also preventing any external AC line noise from entering the PSU. And finally a 7 blade 120mm brushless fan manufactured by ADDA keeps everything cool.

This fan carries a model number of AD1212HB-A71GL and is actually the very same fan used inside the HX620W. Lets check out the specs:

Model: AD1212HB-A71GL
Size: 120mm x 120mm x 25mm
CFM: 85.2cfm
dBA: 39.1dba
RPM: 2200rpm

During a recent conversation with Corsair they tell me that the fan profile for the HX650w has been adjusted to be even quieter than the HX620W. This is probably owing to the (hopefully) higher efficiency of the HX650W with less energy being wasted as heat.

Corsair HX650w 650W ATX PSU Page: 4

Corsair HX650w

To provide accurate and consistent results in all of our PSU testing, Overclock3D uses professional grade DC electronic load equipment capable of placing a sustained load of 3690w across a total of six rails (including +5vsb and -12v) on the PSU!

This is achieved by using a combination of SunMoon and Analogic electronic load equipment which allow us to adjust amperage loads in increments as small as 0.01A while also measuring voltage and wattage readings on-screen.

During today's tests, we will be placing the Corsair HX650w under 25%, 50%, 75% and 100% load levels inside a hot box regulated to a temperature of around 50°C. Additional 'Cross Load' and a 'Max Load' tests will also be performed under these conditions to simulate how the PSU reacts to heavily uneven loads as well as running above its specified output.   

Corsair HX650w Results @ 50°C
   +3.3v  +5.0v  +12v  +5vSB  -12v  AC Watts /
 DC Watts
 Efficiency  Intake /
Δ Temp
Test 1
5.25A 5.25A 9.50A  0.75A  0.20A 190w /
 86.84% 50.4°C /
3.37v 5.08v 12.10v 5.01v  -11.94v
Test 2
10.50A 10.50A 19.00A 1.50A  0.40A  377w /
 87.26%  50.3°C /
3.34v 5.04v 12.06v 4.97v  -11.95v
Test 3
15.75A 15.75A 28.50A 2.25A  0.60A  567w /
 86.59% 50.2C /
3.30v 5.00v 12.02v 4.93v -12.00v
Test 4
21.00A 21.00A 38.00A 3.00A 0.80A 771w /
84.43%  50.6°C /
3.26v 4.95v 11.96v 4.89v -12.04v
Test 5
21.00A 21.00A 1.00A 0.00A 0.00A 240w /
75.00% 50.8°C /
4.0 °C
3.27v 4.77v 12.12v 5.01v -12.13v
Test 6
 1.00A  1.00A  57.00A  0.00A  0.00A 716w /
87.98%  51.0°C /
3.38v 5.07v 11.96v 5.00v -12.68v
Test 7
 21.00A 21.00A 44.00A  3.00A  0.80A 858w /
84.14%  51.2°C /
3.25v 4.94v 11.96v 4.89v -12.10v
Corsair HX650w Performance Overview
 +3.3v Diff.
 +5.0v Diff.
 +12v Diff.
Avg Effic.
Noise Rating
-3.26%   -2.55% -1.15%  86.28% Low 

Looking first at the performance overview chart directly above, we can see that the HX650w manages an average efficiency of 86% in the standard tests 1-4. This is pretty much in line with Corsair's advertised efficiency of 85% given a small margin of error on our part and Corsair's tendency to under-hype their PSU specs. Of course, this is also the first place where we can truly see a difference between the HX650w and the HX620w, with the latter 'only' achieving ~80% efficiency, which to be fair, was good for its day. Voltage stability is also very reasonable on all of the main rails, with the highest fluctuation of 3.26% being well within acceptable tolerances.

Moving on to the first cross-load scenario in test 5 shows that the HX650w isn't too keen on running without a load on its +12v rail. However, as I've said before, this particular test isn't something likely to be reproduced in a real world scenario (who would buy a 650w PSU to only run it at 180w load on the +3v/+5v rails?). So really the results here are somewhat forgivable. Cross-load test 6 on the other hand needs no forgiveness at all, with the HX650w delivering near on it's full output on the +12v rail alone, and with efficiency results approaching almost 88%!

The final test, is of course the one that every PSU manufacturer fears the most....MAX Load. In this test the PSU is pushed as far as it can go before it either engages its safety features, or spits more flames out of its exhaust grill than the Batmobile. Recently I've had quite a few of the latter, but thankfully the HX650w didn't follow suit and managed to deliver a respectable and sustainable 722w. Attempting to go any higher simply resulted in the PSU shutting down safely. Phew.

Corsair HX650w Scope Results @ 50c
   +3.3v  +5.0v  +12v
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7 (MAX)

Ripple refers to the small fluctuations in voltage that occur in all PSU's on a millisecond scale. Large quantities of ripple on a PSU can damage or kill components in your PC over time and therefore testing a PSU's performance in this area is just as important as any other part. Unfortunately ripple cannot be measured using a standard multimeter and requires a specialist device called an oscilloscope. The results you see above are taken from our Rigol 25Mhz 400MSa/s scope that can save 'screenshots' of its data to a USB memory stick.

ATX specification states that ripple should be no higher than 50mV on the +3.3v/+5v rails and 120mV on the +12v rails, and judging by those flat lines in the screenshots above, the HX650W certainly had no trouble at all meeting these requirements throughout almost all of the tests. Only in the cross-load test 5 does the ripple on the +5v rail hit 70mV, but once again we need to remember that this particular load scenario is highly unlikely to ever be encountered in the real world. The rest of the results on the other hand are exceptional with the +3.3v and +5v rails rarely budging from around 10mV and the +12v rail only hitting 42mV in test 6 when the PSU is already running 70w higher than its rated output. Absolutely awesome work Corsair!

Corsair HX650w 650W ATX PSU Page: 5

Corsair HX650w

"If it aint broke, don't try to fix it...just update it". This phrase (although slightly modified) pretty much sums up what was going through Corsair's heads when they decided to release the HX650w. They knew that they already had one of the most respected PSU's on the market with the HX620w, so why change anything that didn't absolutely need it? The look of the unit was great, the size was just perfect, the modular connectors were a hit. All that really needed updating was the efficiency and maybe a few other minor performance tweaks to prevent any other manufacturer from knocking it off its perch.

And that's all they did.

The HX650w IS in simple terms a HX620w with ~6% higher average efficiency, slightly more stable voltages, and according to Corsair, lower noise output thanks to less energy being wasted as heat.

Additionally the tests over on the previous page also show that the HX650w has awesome ripple suppression, a working set of safety features that kick in at around 720w load and the ability to deliver pretty much its entire 650w output on the +12v rail alone.

As per usual the packaging is second to none, the 7 year warranty included with the HX650w is exactly whats needed to show people that a PSU purchase is for life, not just for Christmas (sigh) and the average retail price of £90-95 is more than acceptable for a PSU of this caliber.

So what is there not to like? Well, I cant deny not being every-so-slightly disappointed when I found out that Corsair didn't opt to use CWT as the OEM for this unit as they did for the amazing HX750w and HX850w models. Why? Simply because the HX750w for example has higher efficiency, even more stable rails and in my opinion a better modular connector interface. Of course, I've already mentioned that Corsair probably didn't want to run the risk of spoiling a good thing, and additionally the CWT units are generally quite a bit more chunky than similar wattage Seasonic variants - so the size of the casing may have not been able to stay the same.

But at the end of the day the HX650w is one great PSU and that's all there is to it.

The Good
- Stable voltages across all rails
- Reasonably high efficiency with an average of around 86%
- Great looks and tasty modular cables
- Excellent ripple suppression
- Max output around 720w
- All Japanese caps.
- 7yr warranty!

The Mediocre
- Not quite as efficient or stable as the HX750w or HX850w
- Didn't like one of the cross-load tests (but as I've said already 3 times, its not likely to be reproduced in real world)

The Bad
- Nothing.

Editors Choice

Thanks to Corsair for sending their latest PSU in for us to torture. Discuss this review in the OC3D forums.