My 9500 had a default vCore of 1.2v and so did quite a few others
My first and third 9600 was stock 1.25v but the second one was stock 1.2v, yours can probably drop volts stock.

By adding expensive GPU and so on with a very poor PSU, you're risking killing and damaging your system hardware any millisecond. It can totally destroy your system and is more important than your parts, it powers them. That's despite you being able to tell or not.