Why Power Cables Affect Sound

Besides pure wires, IMO you need pure plugs. AC plugs made with any brass content are damaging the sound from your speakers.
Once I went to all Furutech Duplex (which are made with pure copper, and use springs to maintain contact, I realized the few plain brass Wattgate plugs were altering the sound, mainly adding a white noise into the upper midrange. With me finally buying Pangea powercords of the XL series, which also say they are pure copper plugs.. The sound is better. (though the gold plated SE Pangea were better and no noticeable haze in upper mids, vs cords with plain brass Wattgate plugs)
I cannot say if bronze is different? tin alloy vs zinc.                                     
Also I may try to make a cord like williewonka suggests.. a spiral.. For a source to start.

One thing always pops up in this thread is that people often talk about AC cable as if it directly carries the audio signal.

Can we at least have a consensus that this simply cannot be true? Otherwise I see absolutely no point for any further discussions.

yang_hong (welcome)
The point of threads like this is (some) folks agree power cables CAN affect the sound coming out of the speakers. They agree better AC power cords can and do change the sound one hears from the stereo.
Now the naysayers all agree this is ’not possible’. So that is the crux of the dispute between the yea-sayers, and the nay-sayers.

The most interesting thing is... Over time, many nay-sayers BECOME yea-sayers once they actually hear the changes power cords can make. I am one of those people. I used to, years ago believe power cords were just wire. Now, to me, they are part of the components.
So I would write that power cords in any of the components, can (but not always do) AFFECT the sound coming out of the speakers. and that is the basic claim of the yea-sayers.
The nay-sayers claim it is not possible for a power cord to affect the sound (except if it is too small, or has too much resistance.. The classic resistance, capacitance, inductance, ampacity.. and nothing else.)
So it would seem you (yang_hong) are in the naysayer camp? Welcome anyway!                   
                          
Added" One point is the folks who generally are hearing differences have rather high end systems. I know for my own ability to hear such differences increased a lot when I upgraded back in 2010. And another big improvement in being able to hear such differences when i upgraded this year.             
Such recent upgrades included from Magnepan 3.6 to 20.7 speakers. Buying a Marantz Sa-10 SACD/DAC. Switching all duplex outlets to Furutech GTX-D..

It could be technically correct that the power cable is not in the signal chain but it can limit and alter the amps ability to accurately reproduce the signal by messing with the power. 

It's not that hard of a concept to wrap one's head around. I've experienced a limiting of the soundstage, dynamics and a general softening of the music, obscuring details, ambience and extension as a result. All of that by use of a lesser power cord than what the situation demands. 

Not in the way that a speaker cable or interconnect can do but in the end, the results were strikingly similar.

All the best,
Nonoise

Other factors related to all power cords affecting sound quality, including tricks of the trade,

1. Type of wall outlet
2. Type of wall outlet cover
3. Elevating or suspending power cord
4. Demagnetizing power cord
5. Ionizing or otherwise removing electric static charge
6. Using a contact enhancer on all electrical contacts
7. Choosing a white cable jacket
8. Judging sound quality only after a burn in period of at least 200 hours unless using a burn in device