Power cable education needed


Hi everyone. I need some education on power cables. I have been reading that a good power cable is vital to a good sounding system. If that is true wouldn’t the companies the make the components include a good power cable to insure their product sounds the best that it can ? Should I evaluate the power cables in all of the components in my system? 
ronboco
Shunyata for me.I have a sigma nr an alpha nr, an alpha digital and several deltas. They sure do make a difference and I’ve compared them to ps audio and analysis plus cords that I also have. My theory is that your system is the sum of its parts, so they more weak (parts) links you improve, the better chance it will be able to achieve its full potential. 
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Do I think expensive power cords are better than the cheaper ones? Well it depends, it is like this as an example, and the number is not necessary accurate either. A $500 PC may improve SQ by 2% from the stocked one. A $5,000 PC may improve another 0.2%. Is it worth it? To some it does. But if you cannot hear the first 2%, considered you’re lucky! 
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