How can power cords make a difference?

Gumby, I would be willing to bet that in a better piece of equipment the power cord never sees the severe changes that you talk about. I do agree that the AC side of the supply does see changes in current demand but if there is sufficient filter capacity just after the rectifiers the greatest demand for power should only be when the amp is powered up. This is true simply because an uncharged capacitor looks electrically like a very low resistance.
Once the caps are charged, the demands of the amp are borne by the filter caps which in turn is charged by the rectified AC from your transformer and power cord. I think that a well designed power supply with a hefty set of caps renders the expensive cords impotent. I do however hear differences with different interconnects and speaker cables.

Stevemj and 702. Until you actually plug a cable into a player like mine and have valid comments about such, I am going to do my best to ignore you. We have beat this topic to death in one way or another on multiple posts. We have literally devoted thousands of words to this and have arrived at exactly where we began.

You and 702 come here to fight, I come to learn about music. There are always people like you who know so much that they have their mind made up before they even begin. You definitely fall into that category. You will eventually learn that there are reasons that cables perform differently, and there may even be a scientific explanation for it (someday).

Until then, I am content with the high performance music that real life experience and long term listening has provided. You will remain content, fighting over theory and numbers. I got the better end of the deal. Your system, based on what you post here, sounds terrible. That should be punishment enough for you, it certainly would be an unacceptable experience for me.

Albert, Brulee, Hdm, and others- We've all gone round and round with these individuals who continue to hold to the rationale that would justify their not obtaining/purchasing "expensive power cords". They continue to refuse to participate in the wonderful world of self experience. Regrettably, they are the only losers (musically speaking of course) with this attitude. The rest of us few will continue to obtain greater levels of enjoyment from our audio systems because we are willing to try and experience for ourselves. I wish them well in their smaller world, where troubling ideas and thoughts are vanquished with the wave of a textbook (I'll bet written from someone else's experience?). It must be comforting to live in a world where ALL is known and so thoroughly understood. I for one will enjoy the company of the few souls who wish to travel the road less often taken. Just one man's opinion.

Power cords make a difference, because they are in series with the AC current that supplies the audio equipment's power supply, with AC electricity.

Many times the power cord has made no difference in my system. If I were somehow brainwashed into believing in the placebo, I would think I heard the difference all the time. But I don't. In my system, the differences are most apparent on my preamp and TV. I've tried different cords on everything else and they don't make too much of a difference.