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Seasonic 850WATT S12D PSU

Seasonic has allways proven to be one of the best PSU manufacturers for computers. Lets find out why while we take a look at the S12D 850Watt PSU.


The power supply is the most important peice of computer hardware we will ever purchase. Having too little of a power supply in our computers, can give us lower performance levels, overheating, lock ups, crashes, to all out torching of our most valued computer components.

One of the manufacturers that has been producing the most top of the line PSU’s is Seasonic. Most hardcore overclockers and enthusists know Seasonic for their effeincy, and power distribution to be top notch and we expect nothing less from the best, to properly power our computer systems.

By sporting a newer DC to DC circuit design and utilizing a 105°C all Japanese capacitors, gives the S12D PSU from Seasonic up to a  90% efficiency rating.

Lets throw the S12D PSU in my newest member of computers “Minor Me”, which houses the newer Intel Core i5 CPU cruising at 4012 GHz, with a ATI Tri Fired HD4870’s.


Specifications & Features

The Seasonic S12D PSU has a lot of unique features that other PSUs don’t have. For insatance the DC- DC conversion, also utilizing a 105°C all Japanese Capacitors. Gives this PSU a rating of almost 90% efficiency.


Looking at the packaging that Seasonic uses for the S12D PSU, jumps right out and grabs your attention. Seasonic also gives us plenty of information about the special features, general specifications about this PSU.

Looking at the back side of the Seasonic S12D PSU packaging. This is where all of the unique features this PSU uses that gives it a high efficiency rating of almost 90%.

What comes inside of the box. The PSU, a molex too two (say that tens times as fast as you can while holding on to your tongue) floppy power connectors, four #6 x 32 machine screws, an instruction manual, and a power cable.

Looking at the molex too two floppy power connectors, with the included four #6 x 32 machine screws, and the included sticker.

Finally we have the PSU itself. This PSU is a non modular design.


Lets start off on the Honeycomb vent on the back side that Seasonic uses to help ventilate this PSU. This should give this PSU plenty of airflow to help keep it cool.

Turning our attention at the 120mm fan that Seasonic uses to keep this PSU cool. We can also make out the aluminum heatsinks inside the unit. I would like to see a PSU manufacturer use all copper heatsinks.

Lets go take a peek at the rating sticker of the S12D PSU. Now looking at this sticker got me a little confused, the specifications lists a 70amps combined rating, but on this rating sticker it lists 2x40amp 12Volt rails. Things that make you go hmmm. Have to shoot Seasonic an email about this.

Looking at bundle of wires out of the S12D PSU. Again this PSU is a non modular design.

Looking at the bottom side of the PSU. I have no idea why, but it was in with the pictures.

This PSU does have fairly long molex connectors, and SATA power cables. Seasonic includes 2 x 3 molex power cables, one of these cables will have a floppy power connector attached to it as well. We have 3 x 3 SATA power cables.

Just a quick look at the SATA power plugs used on the S12D PSU.

The molex power plugs, notice these molex plugs use a easy grip design. The one thing I hate is when I go to remove a molex power plug only to be fighting with it tring to get it unplugged. Using these types of plugs makes unplugging these so much easier


Lets go check out the main 24 pin power cable. This cable is average in length, not to long or to short.

An upclose shot of the plug of the main 24 pin power plug. I should mention this is 20+4 main power plug, so for those still needs only 20 pins just needs to remove the +4 pins can do so.

Seasonic includes two EPS power cables, one is 4×4 type plug the other is a straight leg 8 pin power plug.

The S12D PSU uses 2 6+2 PCI-E power cables, and 2 x 6 pin PCI cables. SHould be more then enough cables to handle a dual Nvidia/ATI video card set up.


What this PSU is powering up as far as a computer.

Testing Methodology

Minor Me
CPU Intel Core i5 750
Motherboard GIGABYTE P55-UD6
Case SIlverStone Raven RV-02
Memory GSkill RipJaw
Video Card’s XFX 4870X2, HIS 4870
Hard Drives Patriot SSD 128 Gig, WesternDigital 160 Gig Backup drive.
CDRom Drive Lite On Blue Ray
Power Supply Seasonic 850W, Silver Stone 1200W
CPU Speeds Used 3990MHz
Operating System Used Microsoft Windows Vista 64
Video Card Cooler
Stock cooled
CPU Cooler
Swiftech GTZ water block

There is only one way to test a PSU and that is to stick it in, load up as many rails as possible. I used LinX to load up the CPU to 100% checked the EPS power cable, then checked the Main 24 pin power cable. Loaded up the video cards by running a continuous loop of 3DMark Vantage measured the PCI-E power cables (all four cables), then also checked the Main 24 pin power cable. For the SATA power cable testing I transferred a large 8 gig game from the SSD to the HDD measured the 3.3Volt, 5Volt, and the 12 Volt lines, then went back to the Main 24 pin power cable. The molex power cables provided me with the ground and I hooked up 5 120mm fans and measured the 12Volt and the 5 Volt lines (like 5 0.26 amp 120mm fans going to do anything to the voltage), I again went back to the Main 24 pin power cable. I then tried to attempt an 100% utilization of the computer, by running orthos x 2 Cores on the CPU, ran 3DMark Vantage on one of the cores of the Core i5 750 CPU, then transferred that same 8 gig game from the HDD back to the SSD where it belongs. Only the lowest voltage recorded will be compared on all power lines, 12 Volt, 3.3Volt, & 5 Volt. Now there is always a margin of error, the moisture in the air (too little too much) can and will change these results, so your results will vary depending on computer system, input voltage, and whether or not you are using a UPS, or a power conditioner. I myself, I am using a Monster Power Power Conditioner on my computers.

How I tested the Seasonic S12D PSU.



Power Rail Seasonic S12D 850W PSU SilverStone 1200W ZEUS
Idle Load Idle Load
Main 3.3v 3.42V 3.43V 3.38V 3.36V
Main 5v  5.14V 5.17V  5.11V 5.13V
Main 12v 12.19V 12.17V 12.21V 12.15V
 EPS 1 12v 12.19V 12.15V 12.22V 12.18V
EPS 2 12v 12.19V 12.17V 12.21V 12.16V
PCI-E 1 12v 12.19V 12.17V 12.20V 12.18V
PCI-E 2 12v 12.20V 12.18V 12.19V 12.15V
PCI-E 3 12v 12.20V 12.17V 12.21V 12.18V
PCI-E 4 12v 12.19V 12.18V 12.20V 12.18V
PCI-E 5 12v N/A N/A 12.20V 12.19V
PCI-E 6 12v N/A N/A 12.19V 12.17V
SATA 12v 12.18V 12.18V 12.20V 12.20V
SATA 5v 5.14V 5.15V 5.12V 5.11V
SATA 3.3v 3.42V 3.44V 3.37V 3.37V
Molex 12v 12.19V 12.19V 12.21V 12.19V
Molex 5v 5.15V 5.15V 5.13V 5.13V

As we can see the Seasonic 850 Watt PSU is more then capable of handling a fairly good sized computer system with ease. Only having a fluctuation of 0.02 Volts on the 12 volt line is exceptional. The 3.3 and the 5 volt lines increased in volatge once I started to load these lines up. It is not uncommon to have this, but it is a rare sight to see. The Seasonic PSU also is one of the first PSU’s to have a strict 3% varience on each of the voltage lines, unlike the normal 5% we seen on so many other PSUs. The only Thing I can see is the 5, 3.3 voltage lines are a tad high but again its not enough to be conserned with. As a PSU age their power out put starts to settle down a bit. I rather be a little over then be under a little bit on a new PSU.


The importance of a good quality PSU has become just as important as the components it is powering. By skimping out on a PSU and or settling for a low line PSU can and will cause problems for us in the future. A lot of times a majority of computer problems can be traced back to the PSU.

Seasonic has been a top manufacturer of PSUs for as long as I can remember. There is a reason why these PSU’s get recommended by almost everyone, these PSU’s simply perform. Looking around for a pricing of this PSU, Newegg has this PSU listed for around 180USD. For some of you paying this price might be a little steep to pay for a PSU. Myself I would pay the extra little extra cash for a PSU that I know that will not fail under the most grueling tasks I put my computer through. Having that peace of mind is worth every penny.

The only real issue I encountered was the length of the SATA cables were a bit short to fully extend to where I needed them to be ran at. Keep in mind this PSU is in a Raven RV-02 chassis and that chassis is a lot longer then a standard everday chassis.

Performance 9
Value 8
Quality 9
Features 8
Innovation 9
We are using a new addition to our scoring system to provide additional feedback beyond a flat score. Please note that the final score isn’t an aggregate average of the new rating system.
Total 8
Pro Cons

Solid & stable voltage lines

Quiet operation

Easy grip Molex connectors.

Cables may have issues reaching on some chassis. This is going to be a chassis specific issue.



Summary: The Seasonic S12D is a top quality PSU that will provide s with the stable power lines that is needed for the most demanding computers.

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