I would argue it's amateur PC builders not speccing the PSU correctly that cause these issues. In prebuilt PCs you don't see such issues because the manufactur

I would argue it's amateur PC builders not speccing the PSU correctly that cause these issues. In prebuilt PCs you don't see such issues because the manufacturer controls everything. They might not make the PSU itself but they will certainly get it made with the right specs. In a home-built PC you need to consider not just the total power (wattage) but also the number of rails and current (amperage) per rail. Exceed that and you will run into stability problems. Also, cheap means you get what you pay for. Get something made by Delta and Seasonic and you will have far fewer problems. Some of the cheap no-name brands don't even specify what kind of rails are in there.