A Supercharge Generator power builds a large amount of Supercharge (estimated 180 per cast, or a bit over 1/56 of the full bar per cast).
Supercharge is only gained if you use these powers in combat. They do not actually have to hit a target (e.g. Impaling Ice have relatively short range but as long as you are in combat it builds Supercharge even if it misses entirely). Conversely, if you damage an object with a Supercharge Generator out of combat, you will not gain Supercharge.