Efficiency is defined by the power output divided by the power input and is usually expressed as a percentage. If a PSU were a 100% efficient (which none are) 600 watts of AC power going in would result in 600 watts of DC power coming out (with no waste heat to dissipate). In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process. Newer revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies and now lists both required and recommended minimum efficiencies.
We measured the AC power input to the two SuperNOVA P2 power supplies with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.
SuperNOVA 650 P2:
The overall efficiency of the EVGA SuperNOVA 650 P2 power supply is very good and easily meets the criteria for 80 Plus Platinum certification while operating on 240VAC but struggled a little while operating on 115 VAC at elevated temperatures. However, this is not a big deal as we frequently see this. The 80 Plus Org certification tests are conducted at room temperature (25°C) and our tests are conducted at elevated temperatures (up to 40°C). Efficiency typically decreases as the temperature increases.
SuperNOVA 750 P2:
The overall efficiency of the EVGA SuperNOVA 750 P2 power supply is also very good and also meets the criteria for 80 Plus Platinum certification.
80 Plus Program
Note: Tests conducted at room temperature (25°C)