hi i got rx 570 4gb cuz it was on sale and got 30 euro psu and its working perfectForget it. You need to change the psu first and foremost.
It doesn't have the extra connectors needed to power even the 6-pin graphics cards. This unit was not designed for gaming setups.
If you can't change the psu first, then don't go any further than GT 1030/RX 550.