You obviously have absolutely no idea how much power is required to provide a meaningful amount of boosted intake pressure. Ideal power values for the compressor side of the turbo on a typical car are around 10-30hp. My MS3 usues roughly 25hp to compress intake charge air at ~300bhp and ~16psi of boost (31psi absolute). Feel free to examine various power/boost pressure values with this calculator:
http://www.engineeringtoolbox.com/horsepower-compressed-air-d_1363.html assume ~1.5 CFM of flow for every 1bhp.
What does 25hp mean in a 12vdc eletrical system? About 1550A of current. That is a serious alternator and wiring, which is totally impractical. Only a high-voltage system like those used in hybrid cars could possibly supply this level of power in a reasonable way, but now you're lugging around a hybrid system (more or less) with no regenerative braking capabilities, so all the recharging comes from what? Another alternator? dc-dc converter? The bottom line is that the electrical systems required to support any meaningful level of electric supercharging is heavy, expensive, and possibly dangerous with a possibly minor gain in performance. Let's leave aside the fact that you'd have to try to interface an electric motor and/or geartrain with something that is spinning at 100,000-200,000rpm.
Need I go on?
Sequential turbochargers, twin-charging (turbo and supercharger together), and variable pitch turbochargers all do what you think an electric supercharger should do for less weight, money, and complexity. Yet we rarely see these systems on production cars because the benefits rarely outweigh the costs.
Do not forget: anything is possible if you have no idea what you're talking about.