Why power cable effect overall syste sound?

I think one of the main points missing here is not that cords and cables make no difference, but that people are preoccupied with them and forget room treatment which I find to be far more important, as I think speaker cables are more important, and interconnects being of high importance. A line conditioner is also important especially for digital and SS equipment. And not to forget, the position of the speakers in the room, the listening position, and a host of other things are so important, cable fixes, all the way up and down the chain are used instead of getting the speakers right in the room. Cables should be used to fine tune the system. Using a measuring system, like a mic to evaluate the sound in the room at 1M, and at the listening position will reveal a lot of the room and characteristics. Don't rely of your Ratshack meter, it is rolled below 50Hz, and above 10K. So, don't go and buy another power cord if you are rolled at 10Khz, it is your meter.
If your room and system is right, and all is right and you hear improvements in your power cords, keep them, use them, and stick by what your hear. Your ears are your experience, so be truthful to that.
Personally, I have heard many power cords in different systems, and in some systems there was a difference, others there was not one of significance. The cords evaluated were the best from Shunyata, Cardas, Audioquest, and many others. Each system will have different RF issues, and others. Trust your ears, not the money spent....
Jallen

Thank you Samuel!!

Samuel,
Thank you a lot for answer. It was very well explained. The high frequency backward noise from digital source is well known issue. That's why for digital source is highly desirable to use shielded AC cord or some cable manufactures insert HF filter prior IEC socket to eliminate antenna effect. But I amaze to hear the impact on pure analog system without any clock source.

I too have experimented with power cables, and they all sound different...not only quieter or less quiet. I find that about 80% of the sound of cables comes from the terminations, not from the cable itself.

I have one of Samuel's cords and some of my own design. They all sound better to my ears than stock cords. Bummed to find out after careful AB tests that Samuel's more expensive cords sound even better with my gear than his company's less expensive cords.

I think Samuel's description of how cables work in relation to power supplies and digital noise in the AC circuits near your gear is pretty good. I also think that it is critical to make sure primary signals in low current ic's, speaker cables and even low power circuits inside your gear are effectively shielded from emf and rfi around the high current cables in the immediate neighborhood. In some ways, it doesn't so much matter what is going on with the many feet of unshielded cable in your walls as long as you are effectively dealing with radiation, interference and noise potentially present in the area directly behind your equipment. This is also why it is commonly suggested that you cross PCs with ic's and sc's at 90 degrees rather than running them in parallel, and never bundle low current and high current cables together.