Apekss :
I thought maybe if it doesn't give as much power as the components need to perform at their best it can be an issue
If the PSU couldn't provide enough power for the system, your PC wouldn't boot, or would start to boot & then "poof", the PSU fails and in so doing often takes other components down with it (the GPU is often the unfortunate victim).
So it's not the PSU which is causing the stuttering/low FPS.