I nit picking (dont know what that means im not an native english speaker) because you are giving bad advise to someone who doesnt know better. If you advise someone to upgrade from an RX570 to an RX580 its just bad advise. Like you said "Trust me the feeling is amazing" what feeling is that?...dont get it. So if you dont know your stuff you shouldnt give advise to someone who trust this platform and goes with his own money buying stuff because of your advise.
Btw. The VRAM if more an 4 GB on the graphics card is mostly imported for gaming on higher resolutions so for an full HD Monitor or his 720p Monitor your GPU upgrade is mostly useless. This is one of my main complains about those ATI Cards they get 8 GB VRAM but they really cant handle high resolutions above 1080 p.
And yes @Topic your CPU is the limiting factor in your Build. Get an new one with an board my advise:
PCPartPicker Part List
Type
Item
Price
CPU
AMD Ryzen 5 2600X 3.6 GHz 6-Core Processor
$148.89 @ OutletPC
Motherboard
MSI B450 TOMAHAWK ATX AM4 Motherboard
$114.89 @ OutletPC
Prices include shipping, taxes, rebates, and discounts
Total (before mail-in rebates)
$283.78
Mail-in rebates
-$20.00
Total
$263.78
Generated by PCPartPicker 2019-08-02 05:45 EDT-0400
An bad power supply can dmg your new stuff...so the answer should be clear. First change the power supply!
I would buy an RX card at this moment...whats your budget for your build and what do you want to accomplish? I would recomment going with an ryzen 5 2600X if you buy an graphicscard...about the same price but munch more power.