Example of a CM Extreme Power 460 PSU. It says 460 on the case but not 460W.
The bad news is on the data plate. If you look just under the chart it says the 'combined power' of those rails shall not exceed 401.5 W
And important rating on the +12V rail of 22Amps is less than you see on some good 380W PSUs.
And if the PSU is a few years old it might not be able to put out as much power as when it was new.