If you are paranoid with your computers you would know better than to buy $40 600w power supplies.....you get what you pay for.
With an HD6570 you can get by with a quality 400w power supply. Since Coolermaster tends to be crap you are fine with the 500w model you have.
Either the Microcenter tech was an idiot or he was trying to make a commission off selling you that Thermaltake power supply or both. If anything Thermaltake is even worse than Coolermaster.
So keep what you have now. If you ever upgrade to a decently powerful video card you will need to upgrade though. Stick with Corsair, Seasonic, PC Power and Cooling, XFX, Silverstone, Enermax, OCZ, and Antec for quality brands.