"Super" means that the subject is "above" as in superstructure, superscript and superintendent. A supercharger is then a charger that's above (presumably in performance) regular chargers.
"To charge" means "to load [a carriage]", "A charge" means "a [carriage] load" -- so while the metaphor is overloaded, it actually seems to applies better to charging a battery than to forcing air into a combustion engine.
A turbocharger, or turbo (colloquialism), from the Greek "τύρβη" (mixing/spinning)
Turbochargers were originally known as a turbosuperchargers when all forced induction devices were classified as superchargers
-- Wikipedia
In other words, the turbocharger was actually the origin of the concept of "turbo" meaning boosted speed/power.
I'm still looking for the origin of the "super" part.