I believe there are also multiple generators, at least larger ones than that was shown. As for what powers them? Perhaps they produce their own power in some capacity, as in once you set them up... they just keep going. In Todd's own words "It just works". Though it's not as if you find the generators out in the wastes, we actually have to use resources to build them. I also noticed something else, when crafting a terminal, you need the hacker perk....and when building a trading stand you need a barter perk...