The PSU has nothing to do with the OS, so that would be fine. The memory...not so simple of a question, for two reasons:
1. I've often tripped activation by swapping memory. You wouldn't have to reinstall, but be prepared to reactivate.
2. If you have a 32 bit OS installed now, and you add enough memory to equal or exceed 4 GB, you won't be able to use it all, and should consider installing an x64 OS.