A bad PSU will usually result in boot problems or general instability - applications or OS crashing, bsod etc particularly when power demand spikes (gaming, heavy disk use etc).

Assuming you’re not running out of RAM, this sounds like a software issue. It could be drivers as others mentioned, some background software interfering or perhaps even malware. As a just in case: have you fiddled with process priorities in task manager?

If you’ve got a spare hdd, you could swap that in and do a clean install of your OS. If the issues remain, it’s a hardware problem, if they disappear then it’s something software or config in your current install