Power Supply efficiency

[Frizzo]

if you have a 500w psu that is rated 80% efficient. if the 12v needs to draw 100w, that means it needs to pull 120 or 125? to actually get 100w , because of heat dissipation?

 

[Outlander_04]

There is no standard way that maufacturers rate their psu's

But reputable brands are rating the output amperages , and that with a little bit of math tells you the wattage

Draw from the wall would be higher due to heat losses

 

[Frizzo]

is what this guy saying in the first few paragraphs accurate?

http://mindyourdecisions.com/blog/2011/03/31/is-an-energy-efficient-power-supply-80-plus-worth-it-for-my-computer/