The key here is quality and not quantity...you could have a 400 watt psu that will still cause you problems. 300 watt seems to be enough for your setup...however if its not a quality psu, then u will run into problems. The power supply is one of the most important component in your system if you ask me. btw, i've seen people run their systems stable on a 250 watt pc power and cooling unit with a much higher system spec than you. It's all about quality. Good luck with your MSI card...I have a MSI Ti4600 on the way soon.