Seasonic X900 SS-900HP 900w PSU

Test Results

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'.
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Most Recent Comments

26-09-2007, 08:01:00

"Seasonic have always been known for their high-end range of silent PSU's. Will their latest 900w beast - the X900 unit live up to their reputation and our expectations?"


26-09-2007, 08:25:32

Quality review as always mate, and what an excellent performer. I'll have the stability and efficiency over other blingy high-powered units any day. Keep up the good work Quote

26-09-2007, 08:25:34

Mr. Smith
Almost 85% efficiency is very impressive.

Shame about the noisy fan, had they placed 2 fans in the unit - one intake, one exhaust - then the fans would not have had to reach full throttle like a single one does...

Quality PSU.Quote

26-09-2007, 08:30:25

Agreed, but you look at the load required (776w) to get it to be audible. Many probably wouldn't even get it to break a sweat.Quote

26-09-2007, 08:36:13

Mr. Smith

I did overlook that rather important detail... Probably why pcp&p is silent - never breaks a sweat, not even benching!

This seems like another PSU for life Quote

26-09-2007, 08:53:21

Yeah it's a very good PSU for sure. As you've pointed out, its unlikely most people will ever hear this unit at full throttle, because it needs some serious load for that to happen.

Of course, if you was hell bent on making it total silent, you could always swap out the fan with a SilenX or something. Not that I'd advise anyone to fiddle inside a PSU Quote

27-09-2007, 03:44:58

Jeeze that is a PCP&C rip off if ever I saw one... the silnecer sprigns to mind when I look at that. Similar internal layout, same exhaust fan and positioning etc. But that is a good thing - more manufacturers like PCP&C mean more stable and quality PSU's. A single rail would have been nice but excellent PSU none the less - whopping efficiency!Quote

27-09-2007, 10:02:33

it looks quality tbh...

i'd stil have a pcp&c over it any day...but i bet its cheaper than the pcp&c equivilant....Quote

27-09-2007, 17:30:53

Nice review, looks like a great little PSU, and don't take little literally lolQuote

27-09-2007, 20:56:23

Good review mate, I like the good/mediocre/bad breakdown in the conclusions section.

I have to say I do like Seasonic PSUs. Quote

28-09-2007, 10:16:45

This looks quite good, I need a new PSU for SLIQuote

28-09-2007, 15:31:34

Originally Posted by name='cube'
Jeeze that is a PCP&C rip off if ever I saw one... the silnecer sprigns to mind when I look at that. Similar internal layout, same exhaust fan and positioning etc. But that is a good thing - more manufacturers like PCP&C mean more stable and quality PSU's. A single rail would have been nice but excellent PSU none the less - whopping efficiency!
Quote from Dave Hammock @

SeaSonic M12 SS-700HM 700W [Performs as a Single +12V Rail PSU.] [Modular]

Up to +12V@56A, Rated@40C, Efficiency up to 85%, 3yr warranty

Corsair HX 620W [Performs as a Single +12V Rail PSU.]

Up to +12V@50A, +5VSB@3A

I think most manufacturers design around multiple rails to stay withing the ATX specification.

BitTech in their review of the Seasonic X900, state the Corsair is actually a 750w psu thats "under-rated" to 620w to guarantee silence. They suggest Seasonic should take the same approach with the X900 i.e. class it as a truly silent/quiet 700w psu. I guess if true in this respect with regards to silence you could argue the pcpwr is more like a corsair a 620w? ...well maybe a bit noisyer Quote

28-09-2007, 15:44:45

appologies if sounding like a troll as this was not intended! did a lot of research before purchasing my Seasonic X900 from for £116.32. This is about the same price as the PCPower Silencer 750 quad.

I can tell you this I am running:

Opteron 175 OC from 2.2 to 2.8GHz

X1900XT Crossfire Master + X1900XTX in crossfire OC to 688/1584 core/mem

2x 10000rpm raptors

2x 500GB WD RE2

2x 320GB WD RE

2x 200GB Seagate


under load the psu is cool and the fan runs idle speeds!Quote

28-09-2007, 15:49:34

Ye that system will only put out about what...300-400w?Quote

28-09-2007, 16:10:17

Originally Posted by name='Kempez'
Ye that system will only put out about what...300-400w?
i was wondering about the output, but I guessed it to be around 400-500. i got the Seasonic to replaced my old PCPower 510 SLI turbo cool. I wasn't having much joy running crossfire. the cards were intermitantly not responding a little to frequently for my liking. this was occurring on a non-overclocked crossfire pc with a hard drive count of 6.Quote

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