Power Supply Unit, its what converts the AC power from the wall into DC which your computer can use.
If it has a 6pin PCIe connector, it should be sufficient.
That being said, if its a generic unit (no 80+ Certification, obscure brand or just unbranded entirely, typically grey, small red switch on the back that isnt the power switch) then I would be inclined too replace it. They tend to be pretty horrible quality.