Seasonic S12D 750 W achieved the same performance from M12D, with the terrific advantage of costing 20% less! The basic difference between the two is the presence of a half modular cabling system on M12D. Although S12D uses less powerful transistors on its active PFC circuit this didn’t reflect a bit on the capacity of this power supply in delivering its labeled power.

The main highlight from S12D is its high efficiency and the use of a DC-DC converter on the secondary (i.e., producing +5 V and +3.3 V outputs from the +12 V output) is proving to be a winner for manufacturing highly efficient power supplies. At a load between 300 W and 450 W you should see efficiency around 87%. Remembering that the 80 Plus organization certified this unit as 80 Plus Silver (88% efficiency under typical load), but they test power supplies at only 23 C, while we test them at least double this temperature (efficiency drops with temperature).

Voltage regulation was one of the another highlight from S12D, 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).

Noise and ripple were also very low. When we were pulling 750 W from this unit noise and ripple at +12 V outputs were below 30% the maximum allowed.

Plus we could pull up to 905 W at 47º C from this unit.

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

Seasonic M12D and S12D are excellent power supplies, with S12D bringing the price tag users were looking for!