It's Magic, It's Magic, It's Magic!!!
I agree with LLanger whole heartedly. I think interconnects in general reach a rediculous level of diminishing returns very quickly. I think after you get past the first level of interconnect and speaker cable upgrades, you will get a much bigger bang for the buck upgrading your equipement. If you are paying $1500 for interconnects, I contend you could pay $150 for a set, and spend the other $1350 upgrading your pre-amp, or one of your sources and make a much bigger improvement in sound.
I have gone down that road several times, and come to that conclusion with speaker cables, and interconnects.
But power cords, that's just MAGIC. Yes you can improve on the ones the manufacturers give you, easily. Get a shielded one, made with excellent condutors and a hospital grade connector (Signal Cable, some PS Audio's come to mind). But come on, if you have a $5000 amp, and you spend $1500 on a power cable??? Don't you think you could spend that $1500 on a better amp and upgrade the sound more? That is if the cable makes a difference at all. I contend IT DOES not, past a certain level.
Buy better upstream gear with your money, or better speakers.