I did not see much of a power reduction when modifying a APC ups with a powdered iron inductor. in fact with a few dozen T-106 green-blue cores (used as chokes in computer power supplies) it actually increased consumption.
saw quite a bit of power reduction from typical ferrite cores as an inductor.
i made a swing choke by taking an "e" core but tilting the core such that the air gap was only on one side. this should provide some inductance even at high current while not saturating the whole core. the core i used was about 1 square inch cross section and something like 8 turns, i forget the gap but it wasn't much.
anyhow most ferrite cores found in smps are suitable. since the bulk of the wasted energy (by total kwh) is at idle, it may not matter much if the core saturates at high current.
gap the core about 1%. this gives a permeability of about 100. so a typical 2" long magnetic path gets a .020" gap
