BC_Programmer,
I went to that site and it mows says something different. Apparently they had read my authoritative post and tinged the rowing considerably.
The quote is from wikipedia.
Lets do an example using their statements.
Let us say one has bough a 800 watt power supply that is PC compatible. They claim up to 80 % efficiency at full power. Doing the math, you would get 800 watts out with a loss of 200 watts expected. A power factor of 0.9 is good.
80+ certification means that the efficiency is 80%
or higher (not up to) with 20%, 50%, and 100% loads. It is not a flat rate. The ceritifcation documents and listings show the rated efficiencies of supplies from each manufacturer, and within each list there is an obvious trend whereby all power supplies are most efficent at around 50% load.
By way of example, the CMPSU-1000HX has a listed efficiency at 20% of 81.06%; thus, drawing 200 watts with this supply will be 81.06% efficient. In comparison, The CMPSU-450VX at 50% load has a listed efficiency of 83.77%.
The 450-Watt CMPSU-450VX is more efficient for loads of 200 Watts than the 1000 Watt CMPSU-1000HX. This is demonstrated with the 80+ certification data.
In general a Power supply will be less efficient at lower loads and at higher loads, with a "sweet spot" at 80%. This can be observed within the chart. I chose Corsair in this case but any manufacturer with a lot of rated supplies will work; All of them list a higher efficiency at 50% than at either 20% or 100%; given that the power supplies themselves have different total wattages, the wattage those percentages map to will differ from supply to supply- a 400 Watt supply will typically be more efficient than a 1000 watt supply at providing 200 watts of power, but a 1000 watt supply will typically be more efficient than a 500 watt supply at delivering 500 watts.
