Seasonic M12D SS-850W PSU

Seasonic M12D 850W PSU

Manufacturer: Seasonic
UK Price (as reviewed): £166.74 (inc. VAT)
US Price (as reviewed): $299.99 (ex. Tax)

We've already taken a first look at the M12D 850W here, however after using it and testing it far more extensively - we've finally tidied it up into a full review for our readers, instead of hopping between two articles.

The M12D 850W has some very strong competition - in fact, the market is almost abnormal with a bevy of high quality, recommendable PSUs from Cooler Master's UCP 900W, Antec's Signature 850W and Enermax's Revolution 85+ PSUs. Seasonic needs to score highly on all fronts to get head and shoulders above the rest.

The 850W power output it's the highest wattage PSU Seasonic has ever launched, whereas everyone else has chased the four digit threshold that arguably very few people care for instead of focusing on the new frontier often referred to as efficiency. In this regard Seasonic's M12D is rated at an impressive 80Plus Silver, achieving 85 to 88 percent efficiency across the 20 to 100 percent load range with a 90 percent upwards PFC.

Seasonic's method of achieving such efficiency is no different than we've seen other high efficiency rated supplies - it uses a DC-DC conversion system for the 3.3V and 5V rails from the main 12V output, instead of having an additional set of full AC-DC power converters. Not only this, but Seasonic is also trying another angle too by giving big marketing kudos to its high quality Sayno Denki fan. Honestly, we're not to surprised because every conversation to date with Seasonic, the company has always maintained the fan quality is as crucial as the hardware inside.


The box is pretty normal although the back has rather "liberal" claims just like the Sesaonic S12-II 500W we reviewed a while ago, where every possible "feature" is suggested to be a benefit: take the "Ultra Ventilation" honeycomb grill for example. Almost every single PSU uses this.

Apply your BS filter too, because its liberal use of the marketing wand, has elaborated some of the claims to just being untrue: I couldn't see a single solid aluminium capped capacitor directly linked to the 12V rails and there's literally only a couple of them in total inside. At the end of the day, it's not the box we care about though.

Getting inside, the PSU comes securely packed with plenty of foam, and included is the power lead, bundle of cables in its own Seasonic branded bag to keep them together. To round things off, there's also the five year warranty card and user manual.