No. This is a scam. Think of what is between the wall socket and the generator plant.
I use tube amplifiers and did not hear any difference in power cords.A lot depends on the equipment used, but it is possible to not only hear differences in power cords, but they can be measured as well.
A variac is required. Run the amp up to full power and measure the power output. Measure the voltage drop across the length of the cord. Reset the variac to compensate for the voltage loss on the cord. Measure the output power again. What is the difference? I have seen power cords rob an amplifier of 30% of its output power. Is there anyone saying that such is not audible?
There are two aspects of power cord performance- the overall voltage drop and the ability to pass high current at high frequencies. The latter is a requirement as power transformers, rectifiers and filter capacitors are used in amps. Power rectifiers only turn on for brief periods of time when the cap voltage is less than the transformer voltage- IOW at the peak of the incoming AC waveform. If the cord can pass current during this brief spike, performance is impaired.
Willemj asks us to think about what's in the wall and beyond- well, ROMEX is pretty high performance, good for in the wall but illegal for use outside of it. That's why we have flexible power cords, but they don't perform as well and that's why there is a power cord market.