manaox2, the power cord you have does not have RF shielding. It is a garden hose with residential wiring, filled with sandblasting medium. I guarantee you it will pick up RF. I could give you a quick demonstration with an amateur radio and a meter. This test would be repeatable by anyone and would have measurable data. If sandblasting medium dampens vibrations that harm the signal, that can be tested as well. Have you ever heard the effect of vibrations in your car stereo? Probably not. Unless you performed extensive upgrades, you car has similarly cheap wiring as Virtual Dynamics uses, with no vibration control. Your car is subject to orders of magnitude more vibration than your home is, so if vibrations make no noticeable difference in your car, they won't at home.
Power cords are not attached directly to an amplification circuit. They are attached to a power supply. First, that goes to a transformer. Then it goes through rectifiers (sometimes tubed, sometimes solid state), capacitors, resistors, sometimes chokes, and sometimes regulated by either tubes or solid state. Can we agree that they are widely varied? What goes into a power supply is massively changed by the time it comes out on the other end. I highly recommend Morgan Jones' book if you want to learn more. Bruce Rozenblit's books are similarly excellent. Anyhow, you can put the output of a power supply on an oscilloscope and have a look at what comes out the other side. I've done this and the power cord makes no difference.
Ask yourself this, how can a piece of wire affect thousands of different power supply designs the same way? They can't. Even if a power cord did something to one particular supply, it probably wouldn't to any of the thousands of other supplies the same way. Taking into account component selection and house wiring, there are as many variations as there are people. Something that makes the same change across millions of examples is not possible.
The simple answer is placebo and mass delusion. Power cords are like Bigfoot; they sound plausible at first. But when you get down to it, hard evidence vanishes. Further, everyone involved in the field eventually turns out to be a hoaxer, scammer, lunatic, etc. Cables are just another field of the paranormal, though rarely recognized as that.