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I have just ordered a 650 W PSU for my computer which previously had a 300 W, in order to install a more powerful graphics card. However, I didn't check whether anything would blow up because it was too high - could there be any issues?

Also, what would I need to check to ensure the PSU would be compatible with all the other components?

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As already answered, having a large PSU is not harmful. However there is a downside. Switch mode power supplies have an optimal operating range, typically about 70-100% of rated power. For computer PSUs that are 80Plus certified for efficiency, that range is expanded down to 20% of full rated power. But if the PC idles at a power draw less than the 20% of full power, the PC will use more electrical power with an overcapacity PSU than with a properly sized PSU. A larger PSU will have higher minimum power consumption. – sawdust Apr 2 '12 at 21:35
up vote 13 down vote accepted

There shouldn't be.

The wattage is the measure of how much power your PSU can deliver. The components will (unless they are faulty) only draw as much as they need.

Having a too low an output PSU will cause the PSU to fail in the first instance, which may cause other components to fail as a side effect.

In relation to your edit - there's not really a "compatibility" issue with power supplies. You can get converters (molex <> sata) and splitters if you need to connect older devices. The main thing to ensure is that the combined power consumption of all your devices (hard drives, motherboard, graphics card etc.) is less than the output of the PSU. With a 650W PSU should have a good buffer.

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Thanks - see edit – pighead10 Apr 2 '12 at 19:57
My new graphics card requirements said it requires "500w or higher" - does that mean it will use 500w, or just a recommended wattage to probably cover all the other ones as well? – pighead10 Apr 2 '12 at 20:28
@PigHead - I would hope that it's to cover for all the other components :) – ChrisF Apr 2 '12 at 20:29

The "W" in 650W refers to the wattage not the voltage. The higher wattage will not cause any problems for your PC

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There's no problem, you can have a PSU way more powerful than needed. In some case it's even recommended.

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