I'm sorry to inform you, but the PSU you bought is not capable of delivering 500W ... it's just another cheap and crappy PSU (like Heden, Advance, LCpower and such) which can be dangerous ...
Here is a word about your PSU :
http://www.expertreviews.co.uk/psus/118103/sumvision-power-x-500wToday, no serious manufacturer will sell (real) 500W PSUs without a PCIe connector ... 600/650W will come with two connectors, 700/800W with four, 1000W with six ...
You can find a few reviews with load test of such PSUs, and that's quite terrible ...
Never neglect PSUs, they are the most important piece of your computer. Never try to save money on it, and always go for well known brands (Corsair, Antec, Seasonic, Fortron, ...). The extra bucks spent on them might save you many more if your components (or even house) gets damaged by a crappy cheaper PSU !