Seasonic M12D SS-850W PSU

Performance Results

We test 20 percent (typical idle), 50 percent (typical usage), 75 percent (high usage) and 100 percent loads with both 3.3/5V weighting and 12V weighting to test the whole rail. Power efficiency and Power Factor Correction (PFC) are both rated where higher is better, and we've also recorded theoretical output wattage in brackets, as well as measured output wattage - which more accurately determines efficiency.


Seasonic easily passes the grade for Silver and its efficiency consistency is considerably impressive when we compare it to other premium brands in this area on the next page. Basically, no matter how this PSU is loaded it's completely consistent - you could throw anything at it and it'll always deliver an impressive efficiency and solid voltages.

As expected, the graphs show all green voltages and while over-volting a touch we prefer this to a slight undervolt. The 5V is a touch low, but at least consistent - even when heavily loaded in the 3.3/5V 100 percent test. The 12V rail loads to nearly 99 percent of the total output is impressive but unsurprising given that the single 12V source inside everything, and the dual rail arrangement (limited by over-current protection (OCP)) works well with the given connectors.

We found the Sanyo Denki fan was very impressive - it's extremely well balanced, and while the ball bearing should give a longer life it also prevents it from being truly silent. Up to 50 percent load - a typical usage value - the PSU is very quiet and very tolerable but still somewhat notable from the ball bearing, then moving to 75 percent load the fan kicks it up a little but overall it's still pretty quiet. The most notable part is a bit of higher pitched bearing noise still which can easily be cancelled by thicker case panelling, although it's unlikely to be heard over other case fans. Up to this point it's all good, but the real disappointment for us was at 100 percent load where the 30 minute stress test (that it easily survived we hasten to add!) showed up the M12-D's one flaw: fan speed attenuation in relation to temperature.

Instead the fan speed is directly linked to load, so despite temperatures being very good, the fan still whizzed up like a hair dryer and was the loudest full load ~850W we've heard to date. Checking the box once again writing this final review, Seasonic rates it loosely at somewhere between 35 to 40dB, but we feel even this number is rather conservative.

Internally we checked the temperature with an IR probe and found the maximum temp to be 43ºC around the main transformer, but mostly 33-37ºC inside - much, much cooler than every PSU chucking out 850W of power. The PSU is rated to 50ºC and the caps 105ºC, which this means Seasonic has rated it to handle more heat, so it's even more surprising that there's no correlation to temperature that would make it quieter.