Here's a funny story. I have generic power cables (and no power conditioner, so dozens of feet of aluminum cable leading to a breaker and then dozens more feet to the power transformer) and no abnormally high hiss (which is to say I have a measured SNL well within spec). How come?
The power you have is probley cleaner than mine, also i might have more interference from radio waves etc than you, theres so many variables.
I missed if you had a power-cleaner.. so I'll address both options:
You do: You believe that your power cable picked up more "dirty power" in a couple of feet than I did in (at least) the 200ft to the nearest transformer (which is far less a power-conditioner than a capicater is)?
You don't: So in the hundreds of feet of very basic power cable you have, you believe the issue is the last couple of feet?
Neither one of those makes sense. What makes sense is either that it was not a hiss (but a buzz or hum. which is indicative of an electrical issue, but not "dirty power"), or that there's another factor involved. .
No power cleaner , it was a hissing sound like static coming though the tweeters, i knew 100% the inference was entering though the power some how some where , i took a punt that a shielded powercord might reduce it and at the same time improve the sound quality i could have returned the power cord and got my money back if it had made no difference so i gave it go, the only varable being the powercord A/B ing them with the device volume at 0, stock cord audioable static louder than music til vol level 4, sheilded power cord static greatly reduced alot softer sounding aswell no longer more audioable than music to vol 1, the difference was too big to be placebo plus i didn't actually care whether the new cord was any better than the stock 1 as i could return it for my money back within 30days.
The sub with the amp behind it used to buzz aswell it was only audioable if you put your ear to it though the power cord didn't solve this, i had a mains block custom made with it's own ground loop that solved the problem, so i know the difference between a buzz/hum ground loop and static from interference.
So essentially you solved a grounding problem?