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) 750 watts of AC power going in would result in 750 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 G2 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 750 G2:
The overall efficiency of the EVGA SuperNOVA 750 G2 power supply is very good and meets the criteria for 80Plus Gold certification, even while operating on 115 VAC and at elevated temperatures.
SuperNOVA 850 G2:
The overall efficiency of the EVGA SuperNOVA 850 G2 power supply is also very good, easily meeting the criteria for 80Plus Gold certification.
80 Plus Program
Note 1: Power Factor ≥0.90 (50% to 100% Load)
Note 2: Tests conducted at room temperature (25°C)