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

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

Guys - this is a complex issue, but broken down into its individual components it's relatively easy to understand.
I've attempted to over-simplify and explain this in the past and got all kinds of negative feedback - so I apologized for causing a controversy and stopped trying to explain the physics, magnetics and electro mechanics, dielectrics, metallurgy and engineering - of signal transmission.
teo_audio - what you stated is true, but you didn't explain the contexts nor did you explain the terms you use so "lay" people could understand them. Reminds me of some professors in grad school. Are you trying to make yourself appear intelligent? Are you trying to sell your cable products? Or are you trying to allow people to understand how things work? Maybe you are being sincere and that's the way you relate to people - if that's the case, my condolences. I would like to see the engineering of your cables.
Long story made short - power cords, interconnects and speaker wire most certainly play a part in system performance. I'm not trying to convince anyone, so please save the banter. 
A system has to be at a high enough fidelity level to reveal the performance difference of each component - not just with equipment, but with set up, room acoustics and source material. "The chain is only as strong as the weakest link" - most of the systems I've experienced were not set up to perform their best, including many high end dealer showroom systems for premier product introductions (some in NYC)! I've been involved in this commodity for more than 35 years (man, I'm old) and I've only experienced a handful of systems that were set up to perform to their best potential. A handful!
Anyone who believes differently is welcome to bring their own wires to my home and I'll blindly switch them into and out of our system. Only prerequisite is you have to agree to report the results here before you visit. I live in the central NJ area.
Every single person who heard our system easily noticed differences when something was changed - especially non-audiophiles. My wife notices and she doesn't pay nearly the attention I do.
Believe whatever you want - again, I'm not trying to persuade anyone. Those with an open mind and willing to learn can gain an understanding of why and how things work with relatively little research.
Many people enjoy their music and system with different objectives, I strive to assemble a system which reproduces the recorded event as it was performed. That is - to have the highest fidelity possible. It's far from perfect but for smaller acoustic venue performances, our system is very convincing. Stated another way - it sounds like the real thing, very close to the real thing - though it will never be mistaken for the real thing. Our son can play his sax in our music room and then we'll play some well recorded sax music and you can see / hear for yourself. To create a system that sounds like real music requires one to listen to live music - and not just on rare occasions. 
So many people state - this is better because it has more pronounced bass, or has a bigger image, or any one of a number of issues that demonstrate they're not using live music as a reference. Good luck with trying to put together a system that conveys the emotion of the music.
Last friend I had over to experience our system, upon first hearing it -  put his face in his hands and kept repeating "Oh My God" because he never heard a system sound like real music. He asked for my help and I told him I'd help him, and he then went out on his own and made expensive equipment purchases that won't allow his system to perform to it's potential. Go figure. I asked if he was happy with his system, he said he was and I sincerely wished him well.
I gave up trying to share and help people. Everyone has their own preconceived notions and is convinced of it. People even dispute each other here on Audiogon instead of having an open forum so concepts can be explained and shared. Sharing experiences and information shouldn't be so difficult, but unfortunately it is.
Best to everyone - I normally don't post such things but I guess the last experience with a fellow audiophile friend prompted this.

I wonder if anyone ever attempted to make a power cord out of spark plug wire.

As an electronics guy here is my opinion
 Take it or leave it.  A power cords whole purpose in life is to supply power.  Many manufacturer's will do a great job in circuit design,  power supply design and for some reason overlook the amperage rating of the power cord to consistantly deliver the needed power without losing the power through resistance loss in heat.  I have seen power cords warm to the touch on high quality power amps.  If you feel any heat anywhere from the plug on down,  then the power cord is under rated. In this forum I would think it can happen often.  Appliance power cords are cheap and you can direct connect them the same depending if they were soldered or used connectors.  To hear the difference it would cost much.  I would be more concerned with conditioning the power having voltage regulation,  RF filtering. Under voltage, over voltage and spike arrestor before looking at the cord. 

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.

To  phd,
Ignore him.  He's just trolling all the cable threads and his posts make no sense.  I think he got nothing better to do.