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***The purpose of this is reference only, simply to relay numbers, that's it.
You have to decide what PSU is best, for how you use your system most.
There are NO opinions & I am NOT recommending any PSU***

Efficiency is dividing DC Watt by AC Watts.
I'm looking at what wattage the PSU is most efficient, not the Efficiency Rating (80+Bronze, Silver, Gold..)
two very different things.

~ I took the last 15 PSUs' {ranging from 300~920Watts} that were given the highest 'Golden Award' by hardwaresecrets dot com.
The two highest Efficiency numbers were used,.. that specific AC wattage was combined then divided by two.

Example #1: 500W PSU
224~340W AC {Highest Efficiency range}
Add 224+340 = 564/2 = 282 ~ Now 282 is right in the middle of the Highest Efficiency of that PSU

Divide 282W by 500W PSU gives .564 of Total PSU Wattage
The .564 {56.4%} represents the Efficiency high point.

I then averaged together all the 15 PSU Efficiency high points,
resulting in an average of .6 of Total PSU Watts ,...or 60%

60% of total Wattage, is the Average Efficiency high point for the 15 PSUs' combined

Yes there are variances in testing methodology for various testers/reviewers, but this gives a ballpark on many current PSUs'.
Obviously every PSU is different, so cross reference tests results, and learn everything you can about the Power Supply that interest you.
Then you can decide what PSU is best, for how you use your system most.

>>One very important aspect you cannot overlook is Low Watt {Idle} Efficiency,..this could be the single most important factor in your PSU decision.

________________________________________________________________________
*Four of the PSUs' had a very broad rage of High Efficiency, I initially had three AC numbers for them,
but decided to drop the low AC Watt number. I used to two higher Watt AC numbers for them.

Lastly,..I know my PSU is slightly oversized for my system, simply got a super deal on it..
Edited by kink - 2/18/11 at 7:25am
 + (13 items)
CPUMotherboardGraphicsRAM
E8400   EVGA 680i SLi P mod. 285FTW G.Skill Pi Blk. 954 @ CL4
Hard DriveOSMonitorPower
Seagate .5T + Samsung 1T yes 2310m 1920x1080 X750 @ \$119
Case
retrofit w/ Panaflo 120x38mm Ultra Quiet & S-Flex
 + (13 items)
CPUMotherboardGraphicsRAM
E8400   EVGA 680i SLi P mod. 285FTW G.Skill Pi Blk. 954 @ CL4
Hard DriveOSMonitorPower
Seagate .5T + Samsung 1T yes 2310m 1920x1080 X750 @ \$119
Case
retrofit w/ Panaflo 120x38mm Ultra Quiet & S-Flex