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The PSU should be fine with most cards at the lower end of the budget but when you start going upto 5700XT and Nvidia 20 series for example I'd consider getting a bit more power as its best to be safe than sorry, I know the 5700XT can be a power hungry card at times
It's a pain but if it needs to be done then so be itI enjoy it as i have abit of OCD with cables
I've had that PSU in my build before paired with an RX470 and all was fine no issues or crashes etc I don't think the RX580 is that power hungry to worry about the 500w PSU
I know a lad with a corsair cx430 psu running a rx470 no problems.
The power needs of a system is a black hole of misinformation. The 500w psu you have is fine. What cpu are you running