With all due respect I'd like to make a technical point of clarification about these devices. They're not passive... it's a unique active circuit which operates in parallel with your power-line so they can't limit current since there's nothing placed in series with your power. The best description of what they do is taken directly from their website:
ADD-Powr technology is Algorithm Digital Defined electrical energy and power. Energy is added to electrical signals and systems. It is unique because it is non-invasive.
- The products generate low frequency electromagnetic fields to affect harmonic energy change audio signals and systems.
- The products condition AC line voltage through a low frequency pulsing action to effect an increase of the energy delivered to the power supplies of system components by .8 to 2.5 dB or more.
This corresponds to an increase of voltage peaks from 1 to 5%.
Instead of inserting a potentially current limiting component between the incoming AC and your components, a pulsed field now re-references, or biases, the AC signal.