Here calculate your loadhttp://www.extreme.outervision.com/psucalculatorlite.jsp
Buy corsair, Seasonic, Antec or other known quality PSU.
Run prime95 & Furmark to establish the stability of your PC...
Prime95 & furmark will stress your PSU. If your PC don't crash in 4 to 8 hours w/o error your setup is good.
Use Hw Monitor to measure the current consumption of your hardware.