Shielded power cords are for sensitive equipment, like what is used in a hospital. The shielding is to keep RF and stray signals from getting to other equipment, not 60Hz EMI (Electro-Magnetic Interference). Braided shielding does almost nothing to block that. Distance is what works best- keep any signal cables that must run parallel to power cabling at least a foot away- more distance is better. If they need to cross paths, make sure it's at a right angle. Otherwise, lay them on the floor and look at the picture- if you see lines or other indication of interference, separate them. If not, leave them alone. Don't bundle the power cord with the rest and it will be fine. I did a job a few years ago- I drilled the hole for the power wiring for whoever did the electrical, left a way to pull the new one through to the equipment and kept it away from my low voltage wiring. The mistake I made was to leave my pull cord for the low voltage wiring in place, as a way to make it easy on myself if I needed to pull something later. DOH!!!! The idiot used my pull cord to snake his Romex up to the equipment, through the 1" hole I was using for all of my low voltage cables. Guess what- no noise or problems with any equipment connected to the cables and it couldn't be any closer than that.
An electrical supply place won't care if you need a cord for a stereo or video system, unless the person you talk to happens to have the same interest- they care about voltage and current for lighting and motors, not theoretical differences in sound and video quality due to some kind of special power cord.
