You could have told them to sod off when you saw what they were doing. You could have stated, "As I pay for my electricity on top of the cost to make an extension - did you bring an independent source of power ?' ...but you didn't.
A reciprocal agreement. (5555555)
Ask SWMBO if she'll even allow to bring your copier to IMM. Ask her well in advance so you don't surprise her at the last moment. "But dah-ling SWMBO, the reason I am taking the copier is that I am 100% in the right on this matter and I refuse to cater to their..." She will undoubtedly not be joining you in your endeavour - take that to the bank.