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

Let think about it.  If you're saying the cable is the last 3ft, then why would a power supply be any different?  That is the power supply is the last one after many miles of cables, just like the power supply cord as the last 3ft, then why a power supply would make a difference at all?

People who are using water analogy and conclude that a power supply cable should not make any difference.  But electrons are not water.  Before you turn on the kitchen faucet, there is no water in the kitchen in the first place.  On the other hand, before you power up your equipment, the electrons ALREADY in the equipment.

Look at the tiny fuse in your equipment.  You intuitively think that it has to be the bottleneck but obviously that is not the case.  Now if you're using a power supply cable as tiny as the fuse, things won't be very good.  Your equipment may not work properly.  Why is it that a fuse can be tiny and slim, but not the power cable?  Because electrons are not as intuitive as you think.

You're asking why is a power supply different than a cable?  I didn't  notice anyone mention water but you. The power supply effectivly stops RF getting in and out with electrostatic screens between the primary and secondary in the transformer. As long as the power cord is of sufficient quality to provide the required current to the component that's all you need. 

@andy2 .
Interesting point. Considering how all that current has to flow through a 'tiny' fuse, yet a big honking power cord can still make a change to the overall sound still boggles my mind.
B

I understand that many subjects have already been discussed many times over the years.  However, many times, it is difficult to surf through the years of posts to find adequate responses.  So, it really isn't a problem for a new audiophile to post a topic that has been discussed several times previously.

If you can lead the person to earlier posts, then fine.  If not, then it serves no real purpose rubbing it into their face that this has been discussed many times.  That person was not here then.

In any case, Power Cords are basic.  Then first must be able to handle with margins the voltage and current requirements.  That is mandatory.  In addition is the impedance of the cable.  This impedance varies over frequency.  This is the real problem.  If the interconnecting and terminating equipment isn't designed to handle this variation in cable impedance over frequency, then this is what really effects (afftects?) the signal and the sound.  And yes, this is indeed measurable.

Cable and transmission line science is known and has been around for many decades.

This is really why different cables may make the same system sound different.  Also, I can't recall if most cable manufacturers actually list the impedance of cables over frequency.  This, to me would be the most helpful of information.

This is also why some companies have "networks" attached to cables.  They are designed to minimize the impedance of the cables over the frequency range. Over certain frequencies, it provides for "resonance".  in other words, the impedance due to inductance of the cable negates the "impedance" due to the capacitance of the cable and you are left (hopefully) with an unchanging minimum resistance value.

So, yes, cable can and do make a significant difference in sound quality of the system.  However, It does also depend on how well designed or how poorly designed was the interconnecting equipment and whether they can handle the changes in cable impedance over frequency.

Another reason why some equipment manufacturers "recommend" certain cables.  They've tested their equipment with certain cables, so they know.

A quick bit of history and humor.  I purchased years ago a Mark Levinson 23.5 amp used.  It arrived with the incorrect power cord.  It sounded as if the singer was literally being strangled.  I contacted the seller and he realized that he shipped the wrong power cord with the amp.  He sent the correct cord and all was well.

I was in Stereo Design in San Diego years ago with friends listening to their top system.  It was great.  The representative quickly changed one set of interconnect cables for another and it was like he changed speakers.

I'm an Electrical/Electronics Engineer.  So was my friend.  This made no sense to us, until we thought it through.  So yes, cables do make a difference.

My view is that if I listened to a piece of equipment in the store with manufacturer supplied cable, then that's fine for me in my home system.  But, typically, the stores use much better or more expensive cabling in the top demonstration systems.  Which they should be telling us and at a minimum also demo the equipment with the cord that will be supplied with the equipment so we can make an educated and economic decision at that time.

just my thoughts.

enjoy