Electric Fence Chargers?

I believe that if you look at the pulse on a scope, you would get about the same voltage output because you don't want to jump the insulators. The length of the pulse will be longer to get the attention of cattle like Angus that are better insulated. They might feel a tickle from the 1 joule unit whereas they will get a rude awakening from the 8 joule unit. Listening would give you a indication that most units would give a tick-tick sound vs a buzz-buzz sound for the high powered ones.