Seasonic X900 SS-900HP 900w PSU Page: 1

Over the past 30 years Seasonic have gained a reputation for manufacturing some of the most silent and stable power supplies in the market. With models such as the S12 as part of their portfolio, Seasonic will always be one of the first names mentioned to those seeking silence without compromising performance.

Back in November 06, we were given the chance to test their first ever modular PSU:- the M12. With unique modular cables and decent performance the M12 design was head-hunted by memory giants Corsair. After some minor alterations to the cooling layout of the M12, Corsair released the unit as their now extremely popular HX series.

With more and more high-powered units entering the market from a whole range of manufacturers it's hard to stay with the same product for too long, and for this reason Seasonic have released a new high-end, performance orientated unit named the X900. The X900 power supply is (not surprisingly) rated at 900w, has quad PCI-E connectors and most interestingly of all - an 80mm fan. Today I'll be putting this unit though its paces, comparing its performance to other similar units and finding out if Seasonic have managed to keep their finger on the pulse since the release of their last PSU almost a year ago.

What Seasonic Say:

Since the incorporation of Sea Sonic Electronics Co., Ltd. in 1975, we have maintained our focus on research and development and the production of quality power conversion products.

For the past decades, supported by cutting edge technology based upon a strong research and development team, Sea Sonic Electronics has provided timely and professional solutions to meet many of the IT industry's requirements.

For the future, we will continue our philosophy of dedication; innovation, professionalism and 4G's (Great Technology, Great Quality, Great Service & Great Price) in order to maintain our goal of continued long-term business partnerships and create "win-win" situations for our customers.


The following information has been taken directly from Seasonic's recent press release and Nanopoint's (Seasonic's UK Distributor) website:

Seasonic X900 Power Supply – Ultimate Power & Performance

The Seasonic X900 is designed and built for power, performance, stability and reliability as demanded by power users, gamers and over-clockers. The X900 is a true 900W output power unit with a peak output of over 1,000 watts.

Seasonic X900 is equipped with multiple +12V rails to support high-end graphic cards’ need with a total power output of 72 amps. A Double Forward Converter circuit design achieves a 99% Active Power Factor Correction and an industry-leading efficiency rating of up to 88%. Additionally, the power supply utilizes a Dual Magnetic Amplifier circuit to maintain a class-leading 3% line regulation tolerance on all +12V output rails to meet the demands of high-end graphics cards, CPU’s and peripherals for accurate and stable power output.


• Super high efficiency for energy savings, up to 88% efficiency
• 3% line regulation for +12v rails for maximum stability, security and performance.
• Multiple 12V outputs with enhanced +12V current capability to broaden utilization capabilities.
• High reliability aluminium electrolytic capacitors for increased product life and reliability.
• Active power factor correction [99% PF] for reduced line noise and power distortion.
• Advanced dual forward converter circuit design for added reliability and efficiency.
• Smart and silent fan control [S2FC], one of the best-performance noise controllers available on the market.
• 8cm double ball bearing fan for increased lifetime.
• 4x PCI-Express connectors to support high-end graphic cards. With 6p to 8p PCI-E adapters x2
• All in one DC cabling to support PC, IPC, workstations, servers and dual CPU systems.
• Patented easy swap peripheral connectors for easy plug and unplug connection.
• Total protection with Over Voltage, Over Power and Short Circuit protection.
• Fixed 220V AC input.
• >100,000 hours MTBF, excluding fan.
• RoHS compliant.
• PFC harmonics compliant, EN61000-3-2: 2000
• EMI/ EMC: CE, C-tick & safety approvals: CB, TUV & Semko

As we can see from the specifications above, the X900 provides support for the latest 8-Pin PCI-E powered graphics cards along with multiple +12v rails that Seasonic tout as offering enhanced stability, security and performance.

In addition to this, the X900 is rated at a whopping 88% efficiency. If these figures are indeed confirmed in our testing, this will make the X900 the most efficient PSU we've ever tested!

Seasonic X900 Specs

The X900 has a total of four +12v rails, each rated at 18 amps. This may not seem very impressive considering lower wattage PSU's such as the Tagan 2-Force II 700w quote output of 20 amps across four rails, but what we need to keep in mind is the total combined output of the unit. In the case of the X900 the total combined output is a whopping 72 amps, whereas units such as the Tagan may only be able to produce around 50 amps.

Seasonic X900 SS-900HP 900w PSU Page: 2

With the X900 being Seasonic's latest flagship PSU, it's obvious that they wanted the quality of the unit to be reflected in the design of the packaging. Using only a black and blue 'glow effect' background with a single picture of the unit on the top of the box, they have certainly achieved a simplistic yet professional look.

Seasonic X900 Packaging Seasonic X900 Packaging

Seasonic X900 Packaging Seasonic X900 Packaging

The top and sides of the packaging provide very little information on the unit, leaving potential buyers thirsty for even the most basic of specifications. Thankfully a quick flip of the box reveals a full specs listing in four languages along with a table detailing the nominal and peak output of the unit, and a breakdown of the power distribution amongst its 8 rails.

Seasonic X900 Open Packaging Seasonic X900 Contents

Seasonic have packaged the X900 inside a single walled cardboard box, with an inner cardboard separator box that keeps the main unit apart fom the accessories pack and mains lead. The unit itself is protected from scratches and other minor damage by a fitted bubblewrap bag.

Not wanting to leave you feeling short changed, Seasonic have included the following accessories in addition to the usual PSU, Manual and power lead affair:

- Seasonic case badge.
- 2x PCI-E 6-Pin to 8-Pin convertor cables.
- 1x Molex to Floppy cable.
- 3x Cable ties (re-usable).


Measuring in at 180mm long, the X900 isn't much bigger than your average ATX power supply. This is great news for those of us with small cases or limited space around the PSU area. However, previous high-wattage unit's we've tested around this size have all suffered from overheating issues or poor performance, so it will definitely be interesting to see if Seasonic have managed to avoid these pitfalls in the compact PSU's design.

Seasonic X900 Back Seasonic X900 Front

In keeping with the professional design of the X900 packaging, Seasonic have opted for a plain black powder coated finish on the unit. This ensures that the unit will be an appealing option to those who put functionality higher than appearance on their list of priorities when searching for a new PSU.

As we can see from the images above, the X900 is cooled by a single 80mm fan placed at the rear of the unit. The fan is configured to draw air from the inside of the PC case through the grills at the front of the unit, over the aluminium heatsinks, and exhaust the hot air out the back of your PC with a fair amount of force.

Seasonic X900 Side Seasonic X900 Side

As you'd expect, Seasonic have placed a specification sticker on the side of the unit that mirrors a lot of the information found on the PSU packaging. Around the other side of the unit is a small grill that provides additional airflow to some of the hotter areas inside the PSU.

Seasonic X900 SS-900HP 900w PSU Page: 3
Internal Components

In the past, many people have judged the quality of a PSU on its weight and size of internal components. However, with many manufacturers moving on to newer and more efficient ways of designing their PSU's, it has become increasingly obvious that this is no longer a reliable method for gauging a power supply's quality. By looking inside the X900 we should be able to identify some of the components used and get a good feel for the overall build quality of the unit.

Seasonic X900 Insides

On opening the X900 the first thing that stands out is the large aluminium heatsinks responsible for cooling the the two banks of mosfets attached to them. Sandwiched between the heatsinks are two transformers and a capacitor. The larger of the two transformers (left) is most likely responsible for the +12v rails, with the smaller transformer (upper-right) responsible for both the +3.3v and +5v rails. At the centre is a large black capacitor manufactured by Japanese company Nippon Chemi-con.

Seasonic X900 Inside Seasonic X900 Inside

The overall layout of the X900 is fairly spacious, with plenty of room between the 80mm fan and component board to prevent any cooling dead spots. The aluminium heatsinks are finned in a way that aids the flow of air through the unit and all cables are bundled together with zip ties, giving the inside of the unit a very tidy appearance.

Seasonic X900 Fan

With many PSU manufacturers designing their latest models with 120mm fans it seems rather strange why Seasonic, a manufacturer often associated with silence, would opt for an 80mm fan to cool the X900. However, as many previous reviews on Overclock3D have shown, 120mm fans can be just as loud as as their smaller counterparts when not controlled properly. The specifications for the fan used in the X900 can be seen below:

• Model: AD0812UB-A71GL
• Size (mm): 80x80x25
• Bearing: BALL
• Speed (RPM): 3900
• Airflow (CFM): 50.0
• Noise (dBA): 41.0

Cables & Connectors

Both the Molex, PCI-E and motherboard power cables are sleeved up to the very last connector in black mesh and finished off with zip ties covered in black heatshrink tubing. Strangely Seasonic have decided not to sleeve the SATA cables past the first connector, which makes the unit looks slightly untidy - and left me wondering why they didn't complete the job.

Seasonic X900 Cables Seasonic X900 Cables

However, it has to be said that the quality of the sleeving is exceptional and I was also pleasantly surprised to see that Seasonic have opted for 'Easy Grip' molex connectors - making the removal of the connectors from devices easier.

Seasonic X900 PCI-E Cables Seasonic X900 PCI-E Cables

As you'd expect from a high-wattage unit, the X900 comes with a total of four 6-Pin PCI-E connectors for supporting SLI, Quad-SLI and Crossfire configurations. Support for the very latest 8-Pin PCI-E graphics cards is also provided by means of two extension cables included in the accessories pack.

Seasonic X900 ATX Cable Seasonic X900 EPS-12v

The ATX connector on the X900 is native 24-pin. However, as you can see above, a small block of 4 connectors can be broken off to switch the connector to 20-pin. As many motherboards still make use of the P4-12v 4-Pin connector, Seasonic have chosen to include two separate cables for P4-12v (4-pin) and EPS12v (8-pin) standards.

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Load & Efficiency Tests

To provide our readers with the most accurate results, Overclock3D uses a custom built PSU load tester on all reviews. This not only gives much more reliable results than the testing methods employed by other sites, but also allows for all current and future review results to be compared side-by-side.

Efficiency tests are performed by measuring the wattage consumed by the power supply at the mains (Mains Draw) against the power consumed by the OC3D power supply stress tester (PSU Load). These results may not be 100% accurate, but have proven to be extremely close to results obtained from professional equipment.

+3.3v Rail0w33w66w
+5.0v Rail0w50w100w
+12v Rail(s)0w360w600w

Seasonic X900 Load Tests

As we can see from the chart above, the X900 managed extremely good voltage regulation at all load levels. Even when a total load of 766w was applied to the unit, all voltages remained within their 'ideal' values and a maximum fluctuation of 0.06v was observed on the +12v rails.

Seasonic X900 Efficiency Tests

I have to admit that I was extremely skeptical of Seasonic's quote of 88% efficiency. After all, almost all PSU's we've tested here at Overclock3D in the past have barely manage to break the 83% mark. However, even with our non-professional method of calculating efficiency we can see that the X900 performed amazingly, managing just shy of 85% efficiency under full load.

Temperature Testing

In our continuing efforts to make power supply reviews more thorough, rather than simply checking voltage stability, Overclock3D will now be recording the temerature of each PSU as it undergoes testing. Temperature recordings will be taken from the underside of the PSU's outer casing at 0%, 50% and 100% load levels using a laser infrared thermometer in an attempt to gauge how much heat is likely to radiate into the end-users case.

Seasonic X900 Temperature Testing

Under full load it has to be said that the X900 did get slightly warm. However, once the ambient temperature of 25°c has been taken into account, the 15°c increase from 0% to 100% load is fairly average for a PSU of this wattage. This certainly shows that the 80mm fan chosen by Seasonic is up to the task, and without doubt the spacious and well arranged internal layout of the X900 helped keep the temperatures in check too.

Noise Level Recordings

Possibly the hardest part of any PSU review is summarising the level of noise given out by the unit. The threshold for what is considered 'noisy' varies from person to person and therefore what I may consider a quiet unit, another person may consider extremely loud. A common way to resolve this issue is to use a dBA meter to measure the units noise level, however this doesn't take into account the pitch (type) of noise emitted and whether it is likely to irritate end users.

For this reason OC3D records all power supplies at idle and load in wav format for you to make your own informed decisions. All recordings are taken at 30cm away from the PSU and outside of a PC case. You will need to remember that noise levels will be reduced by varying amounts once the PSU has been installed inside your PC enclosure.

0% Load Recording - Download
50% Load Recording - Download
100% Load Recording - Download

As we can hear from the recordings above, the X900 managed to remain very quiet at 0% and 50% (443w) load levels. Only when the load was increased to 100% (766w) did the 80mm fan on the X900 become clearly audible. However, to put things into perspective, even a high-end Quad Core, SLI based PC system would find it difficult to stress the X900 past ~500w, therefore making it unlikely that most users will ever hear the X900 at 'full throttle'.

Seasonic X900 SS-900HP 900w PSU Page: 5

To put it simply, the Seasonic X900 is a wolf in sheep's clothing. Managing to keep the size of the X900 to not much bigger than your average ATX PSU, Seasonic have ensured that the X900 will work in a wide range of PC enclosures from spacious towers down to compact lanboxes.

This combined with the extremely impressive efficiency figures of almost 85% and minimal voltage fluctuation across each of the X900's rails shows Seasonic's dedication to not only manufacturing power supply's with excellent performance, but consideration for the environment and of course your energy bills too!

Currently priced at just under £130 over at Aqua-PC's and Scan, the X900 is at an amazingly good price point that can currently only be matched by lower wattage units from other manufacturers.

AquaPC's Recommended Retailer

The Good
• Very good voltage stability on all rails.
• Extremely high efficiency of almost 85% reported by our equipment.
• Dimensions not much larger than a standard ATX PSU.
• Very competitive pricing for a 900w unit.
• Silent up to and beyond 50% load.
• 4x PCI-E cables and support for the latest 8-Pin PCI-E standard.

The Mediocre
• 80mm fan gets a tad noisy at 100% load.

The Bad
• Nothing to report.

In recognition of these excellent qualities I need to congratulate Seasonic for managing to obtain Overclock3D's "Best In Class" award. This award signifies that the Seasonic X900 900w PSU is considered by Overclock3D to be the best all-round power supply in the 900w and above classification for the month of September, 2007.

Best In Class Award