That is simple: it makes a very positive improvement in the sound. Then, next step, put in a direct line to the outlet you have your amp plugged in to (and of course to the outlet your power conditioner is plugged into as well).
The theory is that almost all power conditioners restrict the current in some way. Even most that claim they don’t. Sounds plausible to me. I don’t care if the theory is correct, the effect has been real… it has been true every time I tried it.