I'm talking about if you have never built a computer before and don't even know what a motherboard is. Its a little overwhelming at first trying to figure out what the best combo is right for you and what is all compatible with it. If you're just copying someone elses build than yeah I guess its not that bad. Sure there are sites like PCpartpicker that help but you have to know it exists first, and also apparently even though it lists a wattage your computer consumes you should probably get at least 300 watts higher than that just to be safe. I almost bought a 400 watt power supply cause it said my computer would consume 220 watts but apparently you should at least get 550.
Alright, here's a bit of knowledge.
There is no hard rule about "300 watts higher".
It's just compensating for a possibility that you buy a power supply from a shitty brand.
If you have a system that consumes 220 watts, a 300 watt power supply would probably run it, if it's not some garbage brand.
If there's one thing people definitely overdo when they build PCs, they buy power supplies that have capacities WAY above their needs.
I mean one of the lowest models of PSUs that EVGA sells (400W) will still run the large majority of single video card systems out there perfectly fine.