@IMNICEE Check this out.. i think you have one like this.. Blueberry 420w psu
yeahh.. it's a single rail..
I have similar PSU (China made) and it's rated at 500w but it can only draw 200+ watts.. overrated
Better replace as soon as possible with a branded/quality one.
My PSU is also crap korean made.. but better than the chinese crap, but soon i will replace it when the time i will have enough budget.. I've been using it for 6 months now..
I don't know why those PC store gave you a crappy PSU..
Maybe to destroy/burn your PC parts and soon you will comeback on that store and buy new parts?? and after that, they will give you another crappy psu after buying new parts.. money money yeah yeah..
(Sorry for my english, but i have a point)