Help Me Explain Power Cables to my Guitar Friends

Guys, I need some help!

I have suggested to some of my guitar geek buddies that they could improve the performance of their tube guitar amps by replacing the power cords. Now, I know that many here already believe in the qualities of upgraded power cords. But I can't convince my guitar buddies; they won't even try it because they say, "You need to show me some scope measuresments before I believe this 'snake oil' stuff about power cords."

Does anybody know of some way you can "measure" power cords that would "demonstrate" that they can improve performance? Help me out here!