Hola mdenari. In your post, you do not mention the brand and model of your new power amps. At their specifications, they say what is their energy consumption. Usually, the power amp is the one who eats more energy than the other components. The preamp, the DVD, the CD, the computer, and other stuff, do not eat a lot of energy.
20A is a lot of energy, and it usually is oversize. When there is demand of energy, the 20A circuit is enough for bigger hungry wattage amps with a very low sensitivity speakers, circa 82dB/2.83V/m.
Usually the manufacture provides the cables that handles their consumption. Power cords are good, if you want to up-grade the ones that came with your power amps. My advice is, listen first the original for some time, and if you are not happy with them, get a borrow cable(s) from a friend or there are some companies, like Cable Company, that they lend to you for some time, to try out the cable(s) that you want. If you are happy with them, then you purchase them, if not, you do a return. Happy listening!