Seasonic S12II-380 Power Supply

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The cooling worked well. Temperature rise remained very modest and did not reach double digits until about 250W output. From 200W to 380W, the temperature rise stayed at about 9~13°C. This suggests a very well cooled PSU despite the low fan speeds.


Upon turn on, the PSU fan started at just below 4V, then stabilized at 4.12 within a couple of minutes. The Sound Pressure Level (SPL) reading was 20 [email protected], which was audible at 1m, but quiet and smooth. There was no audible buzzing from a meter away at any load. When the fan was stopped with a plastic wire tie jammed into the blades, a bit of buzz could be heard from about a foot away, but this was about at the same level as fanless PSUs we've tested; audible buzzing or humming was not an issue with this sample.

The fan noise and voltage remained unchanged in our thermal test rig to 250W output load. This is extremely quiet performance.

Beyond 250W, the fan speed and noise climbed quickly, as expected. The overall noise at high loads were audibly lower than measured on the Corsair VX450W, which employs the same model of fan. The measured SPL of some other tested PSUs are in the comparison table below; the >30 [email protected] readings are highlighted in light green.

Comparison: Various PSUs Noise Vs. Power Output
Seasonic S12II-380
Seasonic S12-430
Corsair VX450W
Antec EarthWatts 430
Zalman ZM600

The above comparison table should not be taken as an absolute. It shows sound pressure levels recorded on SPCR's test platform. The ambient temperature varies a bit, in a range of 20~23°C, and some of the PSUs may have the small advantage of lower ambient temperature during testing. This can help lower the overall noise curve, and more importantly, increase the power level at which the noise starts getting seriously louder. Still, at higher power levels, the temperature in the test box is determined mostly by the load.

In any case, in the above test data, several models are about equally quiet up to ~200W load. It is satisfying to note that the S12II-380 betters the now discontinued S12-430, staying significantly quieter in the range 200W~300W. (However, it must be noted that the S12-430 was tested in an earlier version of the PSU test system which featured an 80mm fan for cooling rather than the 120mm fan now employed; this difference could shift the power load at which thermally controlled fans begin to speed up.) Its close cousin Corsair VX450W does a bit better at 250W and 300W, but while the S12II-380 peaks out at 39 [email protected], the Corsair keeps getting louder, reaching 44 dBA at the same power level, and 50 dBA at 450W. The difference is directly related to the plastic airflow baffle in the Corsair, which increases wind turbulence noise at higher fan speed. The same factor may be responsible for the lower fan speed (and noise) of the Corsair in the 200-300W range; the baffle may help keep it cooler, hence keeping the fan from speeding faster until >300W.

If you want the best noise performance from the S12II-380, use it in a system that draws no more than 250W (DC), and/or ensure that its immediate environmental temperature does not climb much above 30°C. A system with such parameters is not difficult to build today, especially for energy-savvy PC enthusiasts.


Each of these recording start with 6~10 seconds of silence to let you hear the ambient sound of the room, followed by 10 seconds of the product's noise.

  • Seasonic S12II-380 at up to ~200W output, 21 [email protected]: One meter, One foot (30cm)
  • Seasonic S12II-380 at 250W output, 25 [email protected]: One meter, One foot (30cm)
  • Seasonic S12II-380 at 250W output, 31 [email protected]: One meter

Sound Recordings of PSU Comparatives

  • Corsair VX450W at up to ~250W output, 22 [email protected]: One meter, One foot (30cm)
  • Corsair VX450W at 300W, 26 [email protected]: One meter, One foot (30cm)
  • Corsair VX450W at 350W, 35 [email protected]: One meter, One foot (30cm)
  • Mushkin XP-650 at 150W, [email protected]: One meter, One foot (30cm)
  • Silverstone Element Plus ST50EF-Plus at 250W, 25 [email protected]: One meter, One foot (30cm)


These recordings were made with a high resolution, studio quality, digital recording system, then converted to LAME 128kbps encoded MP3s. We've listened long and hard to ensure there is no audible degradation from the original WAV files to these MP3s. They represent a quick snapshot of what we heard during the review. Two recordings of each noise level were made, one from a distance of one meter, and another from one foot away.

The one meter recording is intended to give you an idea of how the subject of this review sound in actual use — one meter is a reasonable typical distance between a computer or computer component and your ear. The recording contains stretches of ambient noise that you can use to judge the relative loudness of the subject. For best results, set your volume control so that the ambient noise is just barely audible. Be aware that very quiet subjects may not be audible — if we couldn't hear it from one meter, chances are we couldn't record it either!

The one foot recording is designed to bring out the fine details of the noise. Use this recording with caution! Although more detailed, it may not represent how the subject sounds in actual use. It is best to listen to this recording after you have listened to the one meter recording.

More details about how we make these recordings can be found in our short article: Audio Recording Methods Revised.


The new Seasonic S12II-380 delivers clean, stable power suitable for many PC systems today. It's among the quietest fan-cooled PSUs we've tested. It is very energy efficient, as expected of its 80 Plus certified status. The sleeved cables are long enough for large cases, and there aren't too many of them so cable management is less of a headache. Judging by this sample, the S12II should be a fine replacement of the S12 series.

This PSU shows its close family resemblance to the Corsair VX450 in almost every way, from the look, to component layout to details of performance. Even more than the VX450W, the Seasonic S12II-380 answers our call for "lower power models for those of us who seek to make a high efficiency, quiet, yet highly capable computer. 300W would be plenty for such a PC in these days of improving CPU efficiency." The very high efficiency at even <40W load makes the S12II-380 suitable even for energy misers. (As an aside, the EcoPC Reviewer in me asks how much more efficient the S12II-330 might be at super low loads. It's a question we'll try to answer in the near future.)

Final words: The Seasonic S12II-380 is extremely quiet, highly efficient, and performs very well. We like it very much.

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SPCR Articles of Related Interest:
Power Supply Fundamentals
Recommended Power Supplies
Power Distribution within Six PCs
SPCR PSU Test Rig V.4
Silverstone Element Plus ST50EF-Plus
Corsair VX450W
Seasonic S12-430

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