|"I didn't know anything about PSUs until I needed one. Didn't want to go for to much power and end up frying my pc"|
Looks like you still don't know much about PSUs. Do you ever read the PC builder articles at Tom's Hardware? They regularly use the Antec EA-380D Green 380W unit in their gaming builds. Why? Because they know it's more than just about wattage - ALL the specs need to be taken into consideration. The Antec unit has an 80% plus efficiency rating, active PFC, combined +12v amperage of 28A, & a 3 yr warranty. Hopefully the 500W unit you chose has similar specs? Whatever you do, make sure to stick with reputable brand names & expect to pay at least $50 for something decent. Here's a few good ones to give you an example of what to look for: http://tinyurl.com/d7rogqv
And how about posting the specs of your current 400W PSU?