What if my power supply is too powerful?
From time to time, people wonder if it is dangerous to have a power supply that is rated much higher than what they actually need.
And, fortunately, it isn't.
The ratings stamped on power supplies are maximums. The power supply will only supply as much power as the system needs, up to those maximums. Anything beyond that, and it may malfunction. But you're not going to burn your house down by purchasing a 500 W supply to run a system that needs 200 W. In fact, people do it all the time. It's perfectly safe.
It may not be tremendously efficient. Power supplies are most efficient within a certain range of output power, and a "500 W" supply may be less efficient at delivering 200 W of power than a "300 W" competitor. But this varies, depending on the type of load and the specifics of the supplies, meaning there are no absolutes.