The death cap, what's it for, what's it do?

Probably the worst video ever posted on YouTube! It should be taken down and redone with the voltage testing done twice with the plug flipped both ways.
He sorta gets on the first amp and shows voltage going to the chassis. Then completely fails on the next couple of amps and proclaims them safe.
Had he flipped the plug he would've gotten wall voltage on the chassis.
I've done the test enough to know that.
Current is whatever the "death cap" passes. Good cap not much but it'll shock you. Shorted cap, if they short? And the strings of your guitar are plugged straight into the wall. Either the neutral or hot depending on how you flip the plug.

Again a very bad video that should be taken down and redone !

 

Thanks guys! I've learned a lot about this circuitry from this and Rob's article. Now about the Fender Reverb unit not having the death cap, I suspect it's because it was meant to be connected to the accessory outlet on the back of Fender's amps, and its polarity would thus always be the same as the amp's. That was likely the thought behind it.