a lot of cheap power supplies dont even provide what they state, when looking for powersupplies amperage/rail, efficeny, wattage, and just general build quality (components used) are all important factors
check out
http://www.jonnyguru.com/ his power supplies are top notch and he even disassembles the units. chances are that if he hasn't reviewed it or a similar model in the same series then its not worth even looking at.
in general PC power & cooling (Silencer) Enermax (Galaxy, Infinity, Liberty), OCZ (GameXStream, EvoStream), Antec (they vary), Seasonic, Corsair, and Silverstone are all going to be good psus.