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

I already stated the technical side.

1. voltage handling capability must be met
2.  Current carrying capability must be met
3.  Impedance (resistance, inductance, capacitance) changes over frequency.  this is the reason why cables that meet 1 & 2 but are different on number three show differences in sound.

These are measurable.  This is known science.  

Same with amps/pre-amps.  If you really want to see why certain pieces operate and hence sound different, even if they have the same WPC, gain, etc.   Look at the transfer function response of that piece over frequency.  That will tell you all you need to know.  

Then, take an amp that "sounds wonderful" vs an amp that is so-so with the same gain, WPC and look at the transfer function response and it is eye opening.

However, most don't design for transfer function response first.  That is what is measured after the prototype is designed or built.

For amps, it is:

1.  input impedance
2.  Output impedance
3.  Gain
4.  input signal level (min/max)
5.  Frequency response
6.  Power output
7.  phase response
8.  Noise level
9.  Distortion
10.  a few other things.

You decide on circuit design/layout and chose the components that suit your goals and go for it.

All of the above are equation based and can be calculated.

For cables, it is similar.  

1.  which material offers the least capacitance and inductance
2.  What is the impedance per foot of the material to be used.

If you can make the cable impedance virtually zero over the frequency range, that is what you really want.  A straight wire with no impedance.  you are basically connecting the terminating equipment directly to the interconnection equipment.    This is Engineering 101.

But, as mentioned, if the interconnecting/terminating equipment is so sensitive in design that a slight change in cable impedance affects the sound, then that is a real problem.  some equipment is so well designed, that it is hard to hear differences in cables.  On others, you really can.

I imagine for some "high end" expensive cables, the impedance over frequency is extremely low.

for power cords, if it can't handle the voltage requirements it is not suitable. If it can't handle the current requirements, it is definitely not suitable.  Lastly, the impedance of this cable (transmission line) has to be really low over the frequency range.

enjoy

djones51, please reread my post, I never said that power cords and the impact they have on our systems can not be measured. Rather I'm not concerned with measurements, only with the way they sound in my system.

Here's my $0.02...

I didn't believe PC could make any difference. (I studied electronics).
Borrowed a cable (Kimber) from a friendly Audio store (Q-Audio in Cambridge, MA). To my and my friend's utter amazement the cable DID make a pretty obvious difference in sound (context: MF M6si, KEF 104/2, AQ CV-8).
Punch line: neither of us preferred that (more veiled) sound. Both of us would characterize the sound as less in-your-face, more veiled, more suited to very long listening sessions w/o getting tired. But both of us preferred the sound with the stock cable. I would still use whatever came with the amp even if I could have the $300 PC for free. But the sound difference was undeniable and an eye-opener for us both.

Think of your cables as antennas. 

ghjuvanni -- Cool! You guys heard a difference and you didn’t like the more expensive, aftermarket power cord alternative. Ah, listening to your ears!