If it isn't quality, 500W is not enough. JonnyGuru did a roundup of bargain bin power supplies, and they had a cheap PSU that said it was rated for 650W die at 184W of load. Most died before rated load, and getting near that point had voltage ripple way outside of ATX specifications.
Can you give us the exact model of the power supply?
Edit: beat me to posting, the Earthwatts are a great line of PSUs, cheap, SeaSonic built and high-efficiency, it will have no problem with your setup.