powercords

@lostinseattle brings up a valid point, if one can hear a difference, then "what is being changed"?
Different cable type....poses different resistance to the signal.
The thousands of feet electricity goes through outside the home do so through certain conductors, and dielectric materials used by the power company. When it enters your home, the impedance changed when the current passes through YOUR power cord (whether lamp cord or boutique).....the impedance of YOUR power cord is different from that of the power company because it uses different materials.
The resistance characteristic a cable poses when getting a signal from A to B determines how a cable sound. Of course, there are some gray areas and unknown, but one cable sounding different from another is a fact and not something made up or imagined. There are tons of cables that sound so similar that our ears can not pick up the difference, but there are some that sound quite different from one another. I feel like I have an idea.  

Many of my cable experiments were done a little over tens years ago. I was most surprised to hear how power cords made the most difference on my CD player, followed by preamp, then amp (tube and SS). At the time, I had access to cables of many different designs and these experiments were eye-opening.
I find cables to have a quantitive effect, if you like the tone of the cable, a longer length will give you more of that tone, especially the warmer sounding ones.