There are some folks selling "electric superchargers" that are pulling a fast scam. There are others that are legitimate. Sure, it is absolutely possible for an electric supercharger to work. If an axial flow fan or centrifugal blower can far exceed the air flow that an engine normally requires. (such as 500cfm for a V8 or 250cfm on a 4 cylinder engine) , then yes, positive pressure can be generated. How much is determined by the POWER of the electric supercharger. A quick determination of the potential power of an electric supercharger is in its current draw and applied voltage (usually 12-14 volts). An eRAM electric supercharger for example runs at near 60amps, so its power draw is near 840watts. Its unrestricted air flow, is near 1000cfm. It has no restriction, vs a normally configured intake tube, which is usually between 2.5 and 3" in diameter, due to its 3.5" diameter and aerodynamically designed construction. In fact, on a flow bench, an eRAM flows as much as a 3" straight pipe! The actual measured positive pressure in stock air box configurations and in cold air intake tubes, is near .5psi. The negative pressure (vacuum) in all air boxes and even cold air intake tubes is also relieved giving a net pressure gain of near 1% (or near 5% gain in density) this translates to 5% gains to the rear wheels in HP.
Now, if you look at most all the electric superchargers, except the eRAM , you see the current ratings of them , falling in the 2-10amp range. This is because these fans are really boat engine bay vent blowers or automotive air conditioning and heating blowers. all of them are not designed for creating pressure and only have between 25 and 100watts of power. Forget simple math here, simple physics say it takes power to create pressure at a given flow rate. If you dont have any power to work with, you certainly cant expect any pressure to be created.
As far as the current capability of most automotive and motorcycle systems. Anywhere between 200 and 500amps are possible for short term duration. The charging system recharges the battery between bursts from a starter starting the car, or even the eRAM working on only full throttle operation for several seconds. charging systems respond by voltage drop on the battery. (the larger the voltage drop on a battery, the more the alternator trys to boost it back up with higher current flow) A quick test of the capabilities of the electrical system is shown on published eRAM tests. Since the voltage applied under running conditions still allows for charging of the battery at near 14volts, there is no issues. Even dual series eRAMs (two units), draw more than 120amps. charging from the alternator is maxed out at near 80amps for small cars, but the battery can handle quite a bit more. In this application with high current draw, the voltage drops to under 12volts for a short duration, but the applied power to generate pressure in the 1.5psi range is in the 1600watt range (thats near 2hp of applied power before losses are calculated)
I hope this clears up some of the misconceptions relating to the electric supercharger. They do work, IF you have a system that can produce pressure at a given flow rate. This means you need a system that draws more than a few watts. You need a system that draws near 800watts if you want it to produce any pressure at all.
Moving forward, there has been work done in the area of DC brushless motors that draw near 250amps and are much more efficient . These motors running axial flow blowers are known to create near 2-3psi. They are quite a bit more expensive, but it certainly shows the potential for electric superchargers in the near future.