Seasonic M12 600w Modular PSU Page: 1

When it comes to silent yet powerful PSU's, Seasonic are always one of the first companies to be mentioned. In business for over 30 years, Seasonic certainly know what they are doing when it comes to manufacturing power supplies.

Just over a year ago Seasonic released their S12 line-up, with models ranging from 430w-600w. These units proved very popular with enthusiasts who wanted stable power along with low noise levels.

With more and more high powered units entering the market from a whole range of manufacturers its hard to stay with the same product for too long, and for this reason Seasonic have released a new range of modular power supplies labelled the M12 series. The M12 series has a total of 3 models: 500w, 600w and 700w, with the 700w model being Quad-SLI certified. Today I'll be taking a look at the middle-of-the-range 600w model to find out if Seasonic can uphold their reputation for power and silence in one package.

What Seasonic say about themselves:
"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."


Having never seen or reviewed a Seasonic product in the past, I wasn't quite sure what to expect in the packaging department. Some manufacturers go for all-out 'bling', with others being more conservative and going for the professional look.

Seasonic M12 600w Packaging Seasonic M12 600w Packaging

Seasonic have chosen to keep things plain and simple, using inoffensive green and yellow colour scheme with a picture of the PSU on the front of the box. Flip the box over and we can see that Seasonic have printed some of the units most notable features. These include: up to 85% efficiency, voltage fluctuation of 3% or less, 3 year warranty, quiet dual fans and much more.

Seasonic M12 600w Packaging Seasonic M12 600w Packaging

On the side of the box Seasonic have placed a specifications sticker that details the amperage output on each of the M12's rails. There are also illustrations on how the dual fan technology works along with a diagram of the modular cabling system.

Seasonic M12 600w Packaging Seasonic M12 600w Packagingq

The M12 is packaged in a single walled cardboard box and is protected from knocks and scratches by a bubble-wrap bag. Hopefully this will be enough to keep the unit safe from the perils of the most brutal couriers.

Included in the box are the following items:
• 4x Silver ATX screws.
• 1x Power cord.
• 1x M12 manual
• 1x Pack of modular cables
• 1x M12 600w PSU

Seasonic M12 600w Modular PSU Page: 2

The following information has been taken directly from Seasonic's PDF datasheet available here.

• Specification compliance: ATX12V v2.2 & EPS12v v2.9
• Support the latest Intel Core 2 Duo / Extreme & AMD AM2
• 80PLUS Certified: over 80% efficiency
• Multiple +12v output
• Double forward converter design
• Dual Magnetic amplifiers
• Dual fan cooling
• Smart & Silent fan control
• Low ripple and noise
• Short circuit protection on all outputs
• Over voltage protection
• Over power protection
• 100% hi-pot test
• 100% burn in, high temperature cycled on/off



The observant among us may have noticed that both the 500w, 600w and 700w models all have the same rated amperage output across all of their rails. However, a closer look shows that combined amperage output (when all rails are placed under load) is quite different between the 3 units. The 500w unit offers a maximum output of 30a across all +12v rails with the 600w and 700w units offering 48a and 56a respectively.

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Seasonic have never been the kind of company to go for funky colours and flashing lights in order to shift their power supplies. As we can see below - this 'no bling' trend has been continued in their M12 series.

Seasonic M12 600w Top Seasonic M12 600w Back

The Seasonic M12 is powder coated in matt black paint and has a minimal amount of shine. Contrasting with the black body is a silver fan grill responsible for protecting the 120mm fan installed on top of the unit.

The back of the unit has the usual honeycomb grill as seen with almost all power supplies that utilise a 120mm fan. This allows for the hot air circulated by the fan to exit out the back of your PC case. You may also notice the abundance of a voltage selection switch. This is because the M12 is able to detect the input voltage (110/240v) and switch accordingly.

Seasonic M12 600w Side Seasonic M12 600w Front

The sides of the M12 are fairly plain, with one side containing a specification sticker detailing the amperage output of each rail on the M12, along with all the usual certifications and warnings about opening the PSU's casing.

The front of the unit offers a fresh talking point - a 60mm fan covered with a silver fan grill. This was put in place to give airflow to the areas of the PSU that the 120mm does not reach, and also to assist in the extraction of hot air through the mesh at the back of the PSU.

Seasonic M12 600w Modular

The front of the unit also sports 7 modular power connectors, 2 of which are dedicated to providing power to PCI-Express cards. Like many other modular units, Seasonic have decided not to make the ATX and P4/EPS power cables modular.

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The modular power supply is one of those inventions that has the PC enthusiast communities split down the middle. Some think that the modular design is a great design - keeping the inside of your PC tidy while also maximising airflow. Others believe that it is unreliable and can cause increased resistance where poor connectors are used. In the end it really comes down to the quality and type of connectors the manufacturer has adopted for the unit and how well they have implemented the design.

Seasonic M12 600w Modular

Seasonic have gone for their own proprietary 5-Pin flat connector design for use with the Molex and SATA connectors, but have stuck with the tried and tested 6-Pin PCI-E style connectors for powering the PCI-E cables. On attempting to plug in one of the SATA cables I encountered an issue where the connector backplane was able to flex, and thus prevented me from inserting the modular cable. A video recording of the issue can be seen here.

After further investigation, I managed to find the cause of the issue. The backplane had been designed to sit in front of a lip on the bottom of the power supply casing (as can be seen here), but somehow had managed to come loose. This may well be an isolated issue, but it would be good to see a more sturdy design implemented as the connectors are often subject to a fair amount of abuse.

Seasonic M12 600w Cables Seasonic M12 600w Cables

A total of 9 modular cables are included in the box, but it is worth noting that only 7 of these can be plugged into the unit at any one time, leaving two of the cables redundant. All connectors on the M12 are finished in black, with the molex connectors adopting the 'easy grip' design. It's also good to see that Seasonic have decided to sleeve all cables right to the very last connector.

As the use of floppy disk drives is now declining, the majority of us no longer require floppy style power connectors and would rather an extra Molex or SATA connector instead. Seasonic have realised this, and decided to make the usage of floppy disk power connectors optional by supplying them on a separate Molex-to-Floppy extension cable.

Seasonic M12 600w EPS12V Seasonic M12 600w ATX

The ATX connector on the M12 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, and thus make it compatible with older motherboards.
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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Looking Inside

My favourite part of any power supply review has to be taking the unit apart and having a poke around inside. By doing this we can usually get a good idea about the quality of components used and how the unit is likely to perform in our tests.

Seasonic M12 600w Inside Seasonic M12 600w Inside

From the images above, we can see that the M12 has two yellow transformers placed on the centre of the board. The larger of the two is most likely responsible for the +12v rails with the smaller being responsible for +3.3v and +5.0v rails. Placed in between the transformers is a single, reasonably sized black capacitor.

Turn the PSU around, and we can see two wire-wound inductors sitting below one of the large 'claw' shaped heatsinks. Inductors perform a similar role to capacitors and assist in providing steady, clean voltage to the components in your computer system.

Seasonic M12 600w Fan Seasonic M12 600w Fan

As previously mentioned, the S12 makes use of two fans manufactured by ADDA (1x120mm and 1x60mm) in order to cool all components inside the unit. The specifications of these fans can be seen below:

Model: AD0612HB-D71GL
Size: 60mm x 60mm x 15mm
CFM: 16.6cfm
dBA: 32.4dba
RPM: 4500rpm

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

More information on ADDA fans can be found here.

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Load Testing

NOTE: The voltage results obtained for the Seasonic M12 unit are deemed to be inaccurate due to a problem discovered with the OC3D testing equipment. The unit is currently in the process of being re-tested.

In order for the results from all current and future PSU reviews to remain fair and comparable, Overclock3D uses a custom built Power Supply load stress tester.

The tester will be placing the following loads on each of the M12's rails:

+3.3v - 20a Load
+5.0v - 20a Load
+12v1 - 10a Load
+12v2 - 10a Load
+12v3 - 10a Load
+12v4 - 10a Load

The results are collected from a Mastech MAS-345 Multimeter which logs its readings via RS232 to a PC.

Seasonic M12 600w +3.3vSeasonic M12 600w +5.0v

The M12 proved to have very stable voltages on its +3.3 and +5v rails when placed under load. No fluctuation what so ever was exhibited on the +5v rail and a minimal amount of fluctuation (0.02v) was seen on the +3.3v rail.

Seasonic M12 600w +12v1Seasonic M12 600w +12v2

Seasonic M12 600w +12v3Seasonic M12 600w +12v4

All of the +12v rails on the M12 told exactly the same story. No change in Idle and Load voltages was seen, placing this power supply among some of the most stable units we've ever tested here at OC3D. I certainly wasn't expecting these kind of results from the M12 and actually tested the unit several times to ensure that our test equipment wasn't faulty!

Efficiency Testing

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

Seasonic M12 600w Efficiency

The M12 was placed under a load of 646 watts. This counts for a total of 107% of the power supplies rated output. At this load, the power supply required 771 watts from the mains. Therefore the efficiency of this power supply can be found by a simple equation: (646 / 771) * 100, which works out to be an efficiency rating of 83.7%.

Noise Testing

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.

Idle Recording - Download
Load Recording - Download

After hearing good things about the Seasonic units with regards to noise levels, I was expecting the M12 to be a very quiet power supply. However, these expectations started to turn into concerns once I had seen the choice of fans used inside the unit. With two fans rated between 32dBA and 39dBA it became hard to see how these could possibly be considered "Super quiet" as stated on the M12's packaging.

At Idle I started to regain faith in Seasonic's "super quiet" marketing, with the M12 being almost totally silent due to both fans running at very low RPM.

However, once the M12 was placed under load the fan speed increased significantly, and as you can probably hear from the recordings above - made the unit really quite loud. Personally I would find it very hard to recommend the M12 to anybody seeking a silent PSU for their computer.

Seasonic M12 600w Modular PSU Page: 7

When it comes to performance, the M12 is one of the most stable units we've ever tested here at Overclock3D. Matched only by the likes of Zippy and PCP&C, the M12 managed 0% fluctuation across all of its +12v rails and only minimal fluctuation on the +3.3v rail. These excellent results are also complimented by the high efficiency of the M12, managing close to 84%.

Unfortunately the M12 isn't perfect and during our testing showed some issues with the design of the modular cabling system. This problem prevented us from utilising all of the modular cable connectors until we took the power supply apart and re-seated the backplane. It would be good to hear from Seasonic regarding this issue, as the fix we performed would not be feasible for the average user.

The Seasonic M12 is available in the UK for around £110 from Komplett.


• Perfect rail stability only seen on the top-end PSU's.
• High efficiency levels.
• Silent when idle or under medium load.
• All cables professionally sleeved.

• Problems with modular cable connector backplane.
• Noisy when placed under full load.
• Unable to plug in all provided modular cables.
• Price slightly higher than some other 600w modular units.


Thanks to Seasonic for providing this unit for review.

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