I really wouldn't risk using some, generic, old PSU. Grab a decent branded one, Corsair do their Value Series VS models for a reasonable price.

Black screen with a 9800Pro usualy means it's dead. Try cleaning the edge connector though.

I second the use of a good quality PSU. This is something that noone should skimp on.
In Dutch there is this saying: Goedkoop is duurkoop, which roughly translates to "When you go too cheap in what you buy, you will end up having spend more money at the end of the road when you could have saved money if you had gone for the initially more expensive option".

In German there is this saying: "Wer billig kauft, kauft zwei Mal."

= "If you buy cheap, you buy twice."

Tetrium wrote on 2020-05-14, 16:57:

Goedkoop is duurkoop, which roughly translates to "When you go too cheap in what you buy, you will end up having spend more money at the end of the road when you could have saved money if you had gone for the initially more expensive option".

I suspected it was a bit more succinct. Google says the translation is more like "A good bargain is a high price." The English expression is "Penny wise and pound foolish."

There was a famous commercial for oil filters in NA. "You can pay me now or pay me later." Spend $4 for a decent oil filter or $200 in repairs.