I have heard a big difference in a mains lead, just the one time, it was a home made lead I bought on here, not expensive at £20.
It's made from tightly twisted solid core to an MK plug and standard iec.
How did it sound compared to the bog standard provided with my Pearl lite?
As Doug Dunlop, bless him would say, like a bag of nails!!
It sounded bloody awful and had to be removed immediately, the bog standard or the Mark Grant I have was much better.
I use the Mark Grant because at least it doesn't sound any worse than the standard lead.