actually yes it does..
usually in good brand psu, it can deliver more than the label (depend on the limiter of course).
for the example:
seasonic ss750 js can deliver almost 950 watt before shutdown.
superflower platinum 550 watt can deliver 700 watt continous power with gold effeciency..
a good 80 bronze psu, can deliver (usually) around 100 watt or more than then label before the rail became fail and full of spike/ripple.
80 silver / gold / platinum psu, actually an bronze psu with underrated wattage in order to reach high effeciency..
that's why, you can pull more power from it to feed your system.
but once again, it depend on psu limiter..