I'm not sure a new PSU would account for that big of a temp difference either. But if you are stressing the PSU to its maximum capacity, that would definitely cause it to run much hotter which would in turn cause your temps inside the case to go up. And if all there is is hot air flowing inside the case, temps will definitely be affected. By how much, I'm not exactly sure, but......... I am willing to test this out if I can find an old PSU that works.