How can a power cable change the sound when they're all plugged into such cheap power cable in the wall? Does anybody have any real science on this? I'm totally open to it but I'm definitely skeptical. I just think that as long as your IEC cable is at least as good of quality as what's in the wall then there's no way to improve on that.
Early B. is spot on. The issue with this question is the same as for quality level of crossover components. What is presented as science is based on the assumption that if something measures the same it must sound the same. The problem with this approach is the question under consideration is not whether there are measurable differences but whether there are audible differences. This is a sensory issue like taste.
The science that studies sensory perception is it's own field with it's own methodologies which are way more complex than a simple A/B test and need to be to control all the variables involved. I've studied this field and, as a dietitian/nutritionist, have been involved in sensory experiments on different qualities of food and how people perceive them. To do this type of research properly is very time consuming and expensive. Before a company expends the type of resources required, they have to determine if the results will increase sales enough to justify the cost. This is referred to as applied science.
In the case of audio, the answer is no. It doesn't matter rigorous the experiments are or what results are found. They will not change anyone's mind. People who are convinced there can't be any difference will be even more sure they are right while people who are willing to try and make their decision for themselves based on their experience will still do so. If they feel there is a difference worth the cost they will buy the item in question. If not, they won't.
In addition to applied science, there is basic science. Basic science seeks to answer questions for the sake of the knowledge and not for a direct profit motive. Basic science is usually funded through grants which can be private or public (tax dollars). Either way, somebody has to pony up the money to conduct the studies. The naysayers will take the stand it is on the industry to pony up and prove their claims. Which, as mentioned earlier, they will never be able to do to the satisfaction of the naysayers nor will they recoup their investment. The industry will say it's the naysayers responsibility to prove their claim that there is no difference. Which they won't do and, just as with industry, people outside their camp won't believe their results either.
So where does that leave us? Right back where we started. If you don't believe there can possibly be any difference, don't buy the product(s). If you think there might be something to a claim, listen for yourself on your own equipment. If you think there is a difference worth the price to you, keep the product. If not, send it back. It's like the old saying goes, "the proof of the pudding is in the eating", or in this case, in the listening.