I've discovered after many years of cable-sceptisism that there are some really big and important things about cables. The same things can, of course, also be said about capacitors, resistors, transistors etc.
1. Huge difference between stranded and solid core wires. Stranded wires always adds some grain in the treble, it makes the midrange unclear and bass wooly.
2. Huge difference in wire gauge. A thin wire sounds a lot brighter than a fat wire.
3. Isolation - I have not experimented with this, but people who experiments with this says, that it's also important.
The best wire I've tried so far is DIY silverfoil with cotton insulation. But what about powercables?