Charyro is correct. With respect to say amps and preamps, if your AC supply voltage is grossly correct and consistent, boutique power cords and power supply conditioners are unnecessary because the amplification devices, tubes or transistors, use DC current which your amp or preamp produces from its power transformer, rectifier and in some cases, its voltage regulator. So if you want to improve the quality of current presented to these amplification devices, you would have to optimize components within the amp or preamp, the power transformer, rectifiier or voltage regulator, not add on external tweaks like boutique power cords or power conditioners.
If Power Cords Don't Matter...
First of all, I don’t own any high-end power cords, mostly because I can’t fit them behind my rack. Second, I am not trying to stir up controversy, as you will see from my question. I understand that the people who believe power cords make no difference argue that once the power gets into the component, the AC is converted to DC and the power supply of the component takes over completely. I think I have that right for the most part. So it that’s true, and it probably is from a traditional EE standpoint, why is it that I have not heard anyone say that power conditioners make no difference? I am not aware of anyone with a decent system ever saying that a Niagara or Triton or Audience teflon conditioner didn’t affect their sound, for good or for bad. So if the EE theory is true, wouldn’t power conditioners make no difference either? I have an Audience AR6T for almost 10 years and I think it made a big difference. BTW - I am not talking about Power Plants, which deal with voltage stabilization, which is a different topic. Obviously, if your AC voltage is way off, it's going to cause problems.