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Basic Power Supply Question

484 Views 3 Replies 3 Participants Last post by  hungarianhc
Forgive me if this is stupid (i know it is, and i think i know the answer...)

The wattage of a power supply doesn't mean it's always pulling that much... right? Like if I build a HTPC with a 500W power supply, and let's just say it's an atom PC using everything integrated (hypothetical - i know not wise), is it still going to pull the standard 20W-ish that an Atom system pulls? Is the wattage just the maximum? THANKS!
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If you operate a PSU at a small fraction of its rated max power, the efficiency will be lower. For example, an 80+ rated power supply does not have to meet the efficiency number at less than 20% of max rating.

So, while it is certainly true that a 500W PSU will NOT draw 500W of power when given a 20W load, it will probably draw more power than an equivalent 80+ rated 250W or 300W power supply.

But even if the efficiency were absolutely awful, say 50%, you would still only be drawing 40W for a 20W load.
Thanks, Jim! Very helpful response!!!
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