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I'm really confused when it comes to power supplies. I'm looking at a 650 Watt, bronze rated power supply.

Does this mean that it is constantly drawing 650 Watts? Or is that how many it pulls in an hour?

I currently have a 500 Watt Antec Earthwatts PSU, and I don't overclock much and have no need for heavy gaming, but it comes in a combo deal.

Am I throwing away my money on electricity, or does a power supply only draw what is needed - what your system is drawing - and not the full 650 Watts all the time?

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up vote 7 down vote accepted

That's its rated output. It will not output more than the load requires. Its input current demand will vary based on the load on its output. So, no, it won't be putting out 650 watts all the time.

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You can easily confirm Dennis' answer. Borrow a device known as a "Kill-o-Watt" from your local power company (most offer them free) and plug your computer into it. It will show you the device's power consumption under various condition. – CarlF Nov 5 '10 at 20:30

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