Generally if you are buying a PSU from a reliable brand, in your case Corsair VX550W, you would expect them to work just fine without worrying. Sometimes PSU turn out to be faulty but that's a case of bad luck!
If the PSU is installed in a working system, it's probably OK. If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby.