Seasonic M12D 750 W is an impressive power supply, being to this date the power supply with the highest efficiency that we’ve ever tested, beating (by just a little bit, let’s be honest) the previous champ Antec Signature 650 W. We could see efficiency above 90% when we pulled up to 60% from the power supply labeled power (i.e. 450 W), at practically 89% when we pulled 80% load (600 W) and 86.5% when we pulled its full 750 W.

The reason why Seasonic M12D 750 W and Antec Signature 650 W achieved efficiency above 90% lies on the chosen design. Instead of having separated rectifiers for each output, these two power supplies produce mainly only one output: +12 V. From this +12 V output a second smaller power supply produces the +5 V and +3.3 V outputs. This is what the manufacturer calls “DC-DC design”, although technically the use of this name itself doesn’t make any sense, as all switching power supplies are DC-DC converters (as they increase and convert the wall voltage into DC before sending to the switching transistors).

Not only this design proved to be superior, but Seasonic decided to use only high-end components inside this unit, which features only Japanese capacitors and solid caps on the DC-DC converter in charge of the + 5 V and +3.3 V outputs.

Voltage stability was another highlight, with all voltages (including -12 V) within 3% from their nominal values, i.e. we saw voltages closer to their nominal values than what allowed by the ATX standard, which specifies a 5% tolerance (10% for -12 V).

We could also pull up to 850 W at 47º C from this unit.

The number of cables is more than enough, but if you plan to build a three-way SLI system you will need to use adaptors, as this power supply comes with “only” four auxiliary video card power connectors (and each very high-end video card uses two of them).

Of course all these superior specs come with a price. Seasonic M12D 750 W costs USD 210 at Newegg.com, which is expensive for a 750 W product, however we are talking about a premium product for users that really want “the best” and are really worrried about saving energy.

If you don’t think paying USD 210 on a power supply makes any sense, there are several good alternatives on the market – but with lower efficiency – Zalman ZM-750HP (USD 155), SilverStone Decathlon 700 W (USD 180), Topower PowerBird 900 W (USD 180) and Antec CP-850 (USD 130, but unfortunately only fits a few cases from Antec), just to name a few. If you really want a premium product, you may be satisfied with Antec Signature 650, which costs USD 170.