Ahh. You are misinformed.
Cpus/gpus always run at 100% ability. Usage is the amount of resources the cpu needs access to in order to get that 100%. It's a measure of how much the cpu uses, not of how much of the cpu is used.
So say a cpu can pre-render 100 frames in a second, it might only need 45% of its Lcache, 45% of the ram bandwidth, 45% of the cores, 45% of the bandwidth of those cores etc in order to get that 100fps. A frame takes time to render, the code has to be deciphered, objects placed, specs on movement sorted, interactives, background etc. That time is a measure of the cpus instructions per clock (IPC), the clock speeds etc, so regardless of the amount of resources used, the cpu can only render 'X' amount of frames per second. Stronger cpus can do more, weaker cpus only do less.
Imagine you need to drink 12oz of water to swallow a pill. Won't make a difference to how fast you drink if I give you a 16oz glass with 12oz in it or a 44oz glass with 12oz in it. You only need 12oz for that 1 pill. Same with a cpu, it might be capable of using 128oz, but if it only needs 12oz, that's what it'll use to render a frame, the amount of frames being a measure of how Fast it can drink, not how Much.
And No, the Corsair RMx is an excellent psu, and perfectly sized for your build. Just how are you deciding its 'very high power usage'?