I've done about a dozen trade shows and have done both of those things, from personal experience. (This anecdote comes up frequently in these discussions and I always wonder where from, because it's not anything like I've seen...)
So the electrical strip thing seems plausible to me.
Granted that was a while ago.
Maybe the world has changed in the last 42 years, and it'd be helpful to qualify stories like these (where the original poster says he is not allowed, present tense) with where and when they've happened.