|To amplify response #1. |
The wattage of a power supply is the amount of power that it is capable of delivering. If a computer is consuming, say, 150W and the PSU is rated at 200W then that is fine. A 400W PSU replacement will still only handle the same 150W but it is capable of more. Clearly the PSU power rating must never be lower than the maximum power drawn and you would normally rate it a little higher so that it is not running flat out.
Having a PSU with a higher wattage rating only changes "capability" so it will not damage anything.
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