I know I am going to be attacked for writing this, but here goes:
Because there are many situational decision influences here and affective judgments are largely subjective, there often is confirmation bias at work among those in the audiophile community (myself included). It is widely recognized by psychologists that people can and do delude themselves to reduce cognitive dissonance. ("I paid all this money so it should sound better - and hey, yeah, it does.")
That said, it is surely possible that how well the characteristics of a cable (say, its capacitance) match the signal input needs of equipment has some affect on the quality of the sound, but I think we get to being ridiculous when we make claims about how the power cable from the wall to the power supply in our equipment (say, an amplifier) can alter the post processing sound we hear from our signal processing electronics.
Recently, I became aware of the audiophile claim that signal cables (e.g., RCA patch cords carrying signal from your preamp to your power amp) need to go through a period of burn-in before the sound is optimized. I can only laugh. When I have pointed out that no scientific theory about electrical conductivity can support that - that wires are known to be physically unchanged from original state after the electrical signal current stops, the retort I heard is that it is not the conductor that needs to be burned-in, but rather the dielectric (insulating jacket) since dielectrics experience polarization in response to an electric field (which is true). To this I have pointed out that dielectrics have relaxation times as physical properties and that, when you cut the electric field, the dielectric returns to its original physical state. I also point out that, in signal conducting cables, the current is so small that dielectric polarization is negligible. If there is any difference, it is not sufficient to exceed the threshold of human perception. And polarization is not permanent, but temporary anyway, so the concept of burn-in makes no sense.
But many audiophiles persist with these outlandish assertions. And, as a trained scientist, I know that delusional disorders are real phenomena. So I have labeled these sound improvement claims that cannot be supported by scientific physical theory with a name: ADD - audiophile delusion disorder.