OK can't resist:
Do powercords make a difference in sound? Yes; no powercord, no sound.
Do they make a difference by upgrading stock power cords in amps, ect versus aftermarket power cords? Don't know, never had a powercord in an amplifier.
If so, can anyone advise a good bang for the buck upgrade? If you find a powercord in an amplifier, remove powercord to improve sound.