How is three feet of magic power cable supposed to upgrade the dozens of feet of standard household wiring in your walls, and the hundreds of feet of ordinary cable connecting your house to the nearest transformer, and the hundreds of miles of ordinary electric grid wiring?
If the power cord on your amp is undersized (unlikely) I could understand that it might make a difference at extreme volume levels--the properly sized cord wouldn't run as warm.
My amps (2-4004 and 2-8008BB, one channel not used in a 7.0 home theater) are connected to the house circuit breaker box using 25 feet of 10 gauge house wiring, and they are supplied by 4 dedicated circuit breakers and 4 duplex outlets. $250 for a three-foot power cord is TOTALLY INSANE. I have less than that in my house wiring upgrade for all four amps. The amps are rated for maximum current draw of under 1500 watts--read the back panel of yours to verify this. What I've described will allow each of the four amps to pull maximum power at the same time, safely, with minimum resistance/impedance/restriction. This system invokes electical engineering principles, not magic 'n' voodoo, to provide appropriate voltage/current to the input of the amps. By the way, I use $3 made-in-USA duplex outlets, not $60 magic duplex outlets. Call your electrician, and make a REAL difference in the power supplied to your amp(s).