Why power cable effect overall syste sound?

Has anyone ever taken the time to go back and compare their chosen after market power cord to the origial power cord after extended listening? Sometimes we can hear a bigger difference by going back.
As I have said before, I have tried numerous power cords and I hear the difference. However, I prefer the original power cords everytime.
There is no doubt that manufacturers select power cords. I owned a 200 watt Levinson amp that came with a huge power cord. The power cord on my Quicksilver Silver 90 monos had a very small power cord similar to a lamp cord. So, it is obvious these products are voiced with the supplied power cord.
I have owned a lot of older Audio Research gear and I love it because their cords were all hard wired. There was no chance of mixing up power cords and another questionable connection is eliminated.
So, when you are doing maintenance and cleaning connections on interconnects and speaker cables do you clean your IEC sockets too?
Most of the supplied power cords on the equipment I have owned were Belden cables. Belden is a large company and wire is their specialty. They have all of the sophisticated equipment you could possibly imagine for testing and evaluating wire and the materials it is made of. Compare this to some guy in his garage producing a power cord that he covered with a braided jacket and finished off with fancy connectors. What equipment do you think he has to ensure his cable is properly manufactured?

Gtfour45, Wow! I didn't realize you are in charge here and all the way from Australia.
What I do realize is that I am in fact entitled to my opinion too and I will post my opinion anytime I feel it is necessary.
It seems we have really hit a sore spot with you. Do you manufacture cables? Do you sell cables?
I am in my 60s and I have a life time of experience in high end audio. I have owned many many systems that would be considered the best in the world. I know the family sound of all of the best known high end brands.
I have recently noticed there are many newcomers to audio and I feel the need to give them straight answers.
On the other hand, you have no feedback here, so, I assume you don't buy anything and you don't sell anything on this site, therefore you are a noncontributor and you have no right to tell Schipo, vernneal, myself or anyone else that we are not allowed to voice our opinion about anything.
Have a nice day.

Grant, Thank you for your informative comments.

Knownothing, First of all I would like to say I have never said power cables don't make a difference. I have tried numerous power cords and I hear the difference in each and every power cord as I do with every speaker wire and interconnect. System resolution would have to be at an all time low not to hear the difference. What I am saying is I prefer the sound of the original power cord. Maybe I have a purist attitude in this respect and obviously I am not alone. If a given system does not sound right I simply look elsewhere.
I have tried after market power cords on all types of equipment. I was only using amplifiers as an example because of the extreme differences in the power cords of the two amplifiers I mentioned and to make my point.
I understand this thread began with "Why power cables effect system sound", but it evolved rather quickly.
Power cords are not the only thing up for debate these days. I recently spoke with two well known amplifier and preamp designer/manufacturers in a discussion about speaker wire and interconnects. Both said they did not take speaker wire that seriously and they felt the interconnect was much more important. Personally I have had a change in speaker wire make or break a system. However, I respected their opinion and it gave me something to think about when one of them said the most important thing for speaker wire is that it is efficient since it is tranfering the power.
In this hobby there is no right or wrong and there is no such thing as a perfect system. What we believe today we may find out is wrong tomorrow. The main thing is that we enjoy the music along the way. Isn't that how we got into this in the first place?

Hifitime, As I mentioned in a previous post, the IEC socket creates another questionable connection. This is why I prefer a hard wired power cord.
The manufacturers are under a terrific amount of pressure by reviewers and dealers to make changes in their products and it is not always for the better.
I recently commented on a post regarding the well respected Dunlavy SC IV speaker system. John Dunlavy did not believe in spikes or cones and he did not believe in bi-wiring his speakers. However, the reviewers and dealers pressured him until he finally gave in and installed bi-wire posts on his speakers. I tried my SC IVs both ways and the speakers were more coherent with single wire with no loss in dynamics.

Bob_bundus, Apparently you have not been paying attention. This has nothing to do with being a "Doubting Thomas".
Even though this is a debate, it can still be an enjoyable debate without rude comments. I have noticed the rude comments are coming from the group who are the believers in the fact that these after-market power cords have actually improved their system. If you realize a true system improvement then there should be a certain level of confidence in the debate. Instead it seems the debate is fueled by doubt and buyer's remorse.
When exotic speaker wire first came on the market I told a friend about the improvement it make in my system. He laughed and said "right, it just speaker wire". I was not offended by his comments because knew what I heard.
I didn't need a technical explanation why it sounded better. I still don't care if it is 99.9999 pure oxygen free copper or silver coated copper or pure silver. I don't care what the dialectric is made of, if somebody froze it or if the spades were connected with some special solderless method. I don't care if it is multple strands or solid core. I don't care what the gauge is or if the jacket is pink or purple. Well, I might care if it is pink.
All I care about is if it sounds good in my system. And if it does sound good in my system, there is no guarantee it will sound good in yours.

Mnnc, I'm glad to hear you found something that improved your system without spending an arm and a leg. Happy listening.