... abit confused: how does a power cord affect the presentation of sound...

IM or intermodulation noise can be reduced below human hearing. Once the random noise floor reaches these levels of -160 dBFS  in a DAC noise from amps, speakers etc.. swamp it. It isn't audible to humans , dolphins maybe. 

The Benchmark DAC3 offers extremely low levels of harmonic distortion from all its outputs. Intermodulation distortion was similarly vanishingly low."

"No power-supply–related spuriae can be seen, and the random noise floor lies below –160 dBFS!"

"When the DAC3 decoded dithered 16-bit and 24-bit data representing a 1 kHz tone at -60 dBFS, the increase in bit depth dropped the noise floor by more than 30 dB, indicating that the Benchmark’s resolution is at least 21 bits."

https://www.avsforum.com/forum/173-2-channel-audio/3061980-rob-watts-dac-design-other-audio-musings.html

It is an interesting video...

He speak about you can hear the difference between noise floor of -200dB vs -175dB.

Perhaps he knows his trade- off business.... :)

My own experince and experiments teach me that some pieces of minerals anywhere all along the electrical grid modify the sound coming from this modification of the noise floor... Discuss with him for brain resolving power in hearing .... :)

I put bags of beach peebles on the external electrical cable of my house and guess what that makes audible difference...

Rob Watts says that even adding a small electronic chips in a dac add noise that is audible by him.... He knows perhaps something....

I will let these arguments here.... I am absolutely not knowledgeable in engineering but i only want to speak about my simple experiments.... I use these experiments to improve my own audio system beyond all expectation.... Believe what you want.... I cannot change beliefs.... I am only interested in simple way too improve my system and it is working astoundingly at peanuts costs....All my controls methods are homemade and i had no scientific explanation for some.... 

:)

Hi @mahgister:

You are 100% right! Nobody can change their beliefs. They will Google the s%#*^t out of Internet to find pseudoscience stuff to support their beliefs. Or is it religion? And forget about listening or trying. They would do nothing of that if it goes against their beliefs. Even if it were free.

.... I cannot change beliefs.... 

«Science is not written in books it is written in nature only» - Anonymus geniuses in history, too many to be named....

« Our powerful ignorance is sometimes named technology»- Groucho Marx

I don't think you understand the meaning of pseudoscience. Why don't you Google it Einstein.