It’s not a scam or anything esoteric, the device actually does what they’re claiming it to do. It’s just that residential users don’t really need it.

A power factor correction device isn’t a battery or other storage unit that puts more power into your system, rather, it works by altering the electrical characteristics of your home to be more favorable to power transmission.

AC power can be visualized as two sine waves - one for current and one for voltage. With no load, or a purely resistive load (most of the devices in your house), the waveforms will be “in phase”. The peak of the current waveform will occur at the same time as the peak of the voltage waveform. Their phase difference will be 0 degrees, and the power factor (the cosine of the phase difference) will be 1, indicating maximum power transmission.

Electric motors, as a side effect of their design, are inductive loads. Inductors, which are coils of wire designed to store energy in a magnetic field, do not allow the current to change instantaneously, because the magnetic field generated by the flowing current induces an opposing current in the inductor (self-inductance). That causes the current to “lag” the voltage. Think of the voltage waveform staying where it is, and the current waveform being “pulled” back - the peaks will no longer match up. In this situation, power is wasted.

The capacitor in the Power Save, or any other power factor correction unit, work to oppose the effects of the inductor. Capacitors, which are devices that store energy in an electric field, do not allow the voltage to change instantaneously. The voltage will “lag” the current. However, since the inductor has already caused the current to lag, the effect of the capacitor will be to “pull” the voltage waveform back in phase with the current waveform, decreasing the phase difference and increasing the power factor.

That’s my understanding of it, at least. If I’m being fuzzy somewhere, then, please help me out.