Let's be logical.
It is possible that active power conditioners affect the sound of the system.
But if you are talking about 6 feet of power cord with no active component, this can have nil effect as long as it's large enough to carry easily the power being drawn by the system.
Think about it. Behind the 6 foot power cord there is a (usually) much longer connection to your meter. Won't that foul up the power? OK you can up-specify that and many of us do. But probably not with wire costing $1,000/foot.
The meter is connected in the street to the local transformer that may be 400 yards or more away. A quarter a mile of wire fouling up your system. You don't own that wire so there is nothing you can do about it, even if you could afford the $400,000 to improve it.
Even if you improve the power cords local to the system, there's a lot more wire carrying your power that you can't touch.
Like bits are bits, in the digital domain at least, power cord is power cord, as long as it's thick enough for the job.
And snake oil is snake oil.
