Seasonic S12II-380 Power Supply

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August 16, 2007 by Mike Chin

Seasonic S12II-380
ATX12V v2.2 / v2.01 power supply
Market Price

Seasonic has a long history of making quiet, efficient, high performance, power supplies. Whether marketed under their own brand name or under others' (such as Corsair Memory and Antec), Seasonic power supplies have become the most popular choice of quiet computing enthusiasts around the world. The consistency over the years has been unmatched, as virtually every Seasonic PSU ever tested by SPCR has scored high marks.

As the brand is such a strong presence among quiet PC enthusiasts, a quick review of their current lineup is worthwhile; it appears to be a time of transitions for Seasonic products:

*S12II 330, 380, 430, 500 - The lineup in which the model under review belongs. All are 80 Plus certified for >80% efficiency. This line replaces the lower rated models of the S12 line, which is now discontinued.

*S12 Energy Plus 550, 650 - High power models 80 Plus certified based on the second generation of the S12 line.

*M12 500, 600, 700 - Detachable cables, 80 Plus certified.

There's talk of a very high power model becoming available in late fall or winter, something around the 900W mark. There may also be modifications and changes to the modular cable M12 line, but details are unavailable as of yet.

The model designation S12 came simply from the size of the fan used in these models: 12 cm. Most readers probably know that until 3~4 years ago, most PSUs sported a single 80mm fan; a few had a second 92mm fan. There were almost no PSUs with 12 cm fans, so the S12 model designation made perfectly good sense.

S12II is obviously a major rework of the original S12, which underwent at least one significant revision during its >two-year life-cycle. (See Seasonic S12-430: Beyond the Super Tornado and Seasonic S12-330 PSU, new sleeved version). Interestingly, the S12II-380 is not our first look at this new series of power supplies from Seasonic. The Corsair VX450W we reviewed a month ago is basically a member of the same series.

The S12II 380 is one of the most modestly rated ATX12V PSUs, not only for Seasonic, but in the retail market today. Median power ratings appear to fall in the 400~500W range these days. Yet, our research shows that no desktop system with a single CPU and a single graphics card demands anywhere near that level of power. The 380W rating of this model may be just about ideal for the vast majority of desktop systems built by DIYers today.

Modest size full color retail package.

The modesty continues inside: The PSU is inside a bubble-plastic bag. There's a user's manual, screws, plastic cable straps, and AC power cable.


Seasonic S12II-380 Feature Highlights (from the web site)
Multiple +12V Outputs - Enhanced +12V current capability broadens utilization possibilities.
Not really multiple 12V line; it has current protection to keep electrical energy in each output wire from exceeding 240VA.
Super High Efficiency [up to 85%] - Optimal solution for low energy consumption, noise & heat. Very good, familiar Seasonic territory.
Double Forward Converter Design - Advanced topology for the highest efficiency.
Ditto (like the above.)
Active Power Factor Correction [99% PF] - Reduces line loss & power distortion. It's a good thing, ecologically speaking, and for the power utilities.
Universal AC Input [Full Range] - Plug & run safely anywhere in the world.
Standard on Seasonics for years now.
Smart & Silent Fan Control [ S²FC] - Smart thermal control to balance noise & cooling.
A key foundation of Seasonic's quiet performance.
Conductive Polymer Aluminum Solid Capacitors - Advanced ultra-low resistance, high temperature capacitors on critical 12V rail.
To assure savvy buyers who may be aware of the bad cap fiasco that's plagued China-made electronics for some years.
Over Current/Voltage/Power Protection, Under Voltage Protection, and Short Circuit Protection. About par for the high end course.
Standard ATX/PS2 size: 150mm(W) x 86mm(H) x 140mm(L) Standard size is good.
MTBF: 100,000 Hours @ 25°C That's a long time. What about at a more realistic 30°C or 35°C?
Safety Approvals: UL, CUL, CE, CB, FCC Class B, TÜV, CCC, C-tick. The more the merrier.
Three year warranty. Good.


Seasonic SS-380GB ouput specifications on label. As with most recent ATX12V PSUs, most of the output capacity is at the 12V line.


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