PSU wattage ratings.

[JonSimonzi]

Now, I understand that a PSU takes in power from the wall, lets say 500w, and doesn't put out all 500w to the computer, which is where the efficiency rating comes in. For the example, we'll say 80% efficiency, so that 500w it takes in, it puts out 400w. Now, if a PSU says it's rated at 750w, is that what it can take in from the outlet, or what it can put out to the computer? Meaning if it's what it can put out to the computer, a 750w PSU with 80% efficiency can pull out about 937.5w from the wall?

 

[Bobnova]

It's the second one, they're rated by what they can put out (in theory, in reality that really depends on the brand, some brands like to slap 750w stickers on 500w PSUs), so the draw from the wall is higher.

 

[deadlysyn]

It's the second one, they're rated by what they can put out (in theory, in reality that really depends on the brand, some brands like to slap 750w stickers on 500w PSUs), so the draw from the wall is higher.

Also, some PSU companies like to crank up the wattage output on the 5 volt and 3.3 volt rails, which is not needed for new systems. I have seen it a lot, considering one of the local shops tries to pass off some kind of cheap garbage PSU's called A-Power. Usually that is what you see wne you have a "750 watt" PSU that is only capable of maybe 450 watts. Usually those PSU's will not be 80+ certified, and are not worth the extremely low price they sell for.

 

[neonblingbling]

500W PSU *should* provide 500W to the computer, drawing more from the wall.

For example, check out the chart in this review. You can see in test 5 that the 850W PSU puts out 844W DC, and sucks 1047W from the wall.