Do you mean increased performance while playing a game? There should be no difference in performance during a gaming session as long as the power supply is capable of delivering the required power to the system.
There is a decrease in performance when a power supply cannot deliver the required power. For example the screen might wobble, then stutter, and finally freeze. The power supply might shut off if there is an overlaod or temperatures get too hot. In a worst case scenario it may blow and fry other components.