The solution for a low-quality power supply is never an AVR, it's a better-quality power supply.
Do you have a picture of the label on the power supply? Because even some of the nastiest junk power supplies out there, you can usually find them somewhere on the web, but I'm not "Supercool Intext" anywhere. While theoretically, some garbage 750W PSUs may be perfectly find 300W PSUs, there's not even enough info to verify this.
Honestly, I'd just replace the nasty thing under any circumstances.