Crezth
i knew you were a real man of the left
Well, the reactor output really depends on the reactor. If you look at stats, it should be clear that some produce more than others. At the moment, it's not safe to say population per energy, because in most cases, the energy ISN'T used for standard use as IRL. Energy is more for one-time things such as jumpstarts and so forth. The exception to this are vaults, which typically all have electricity produced inherently and unrerroutably to power the vital systems.
Not just jumpstarts, but also for powering something up that you really aren't going to power down... such as robots. You're using whatever source you had for energy in doing that.
Given the prevalence of nuclear technology in most of pre-war America (judging by evidence from the games, mostly) I'm going to put in my two cents by saying that these are ubiquitous technologies, and the (adorable) technology of fission batteries certainly belies the fact.
Because of the nature of nuclear energy, I can't imagine why there'd be very much concern about renewable energy, as it is quite obvious that in lieu of any dinosaurs left to burn the Powers That Be went with the best and most green-glowing option. My point in saying this is that, simply, major non-nuclear power plants probably wouldn't really exist in number and that the knowledge for building them is even more lost to the ages than the knowledge for building a nuclear reactor.
Specifically, I mean this: you can walk into dozens of facilities in every game and find nuclear reactors sitting around like pieces of furniture, powering ancient light fixtures as they have done for centuries and still chugging along reliably. To me, this is the most important factor: in fact, most people living in post-apocalyptia shouldn't even know that you could get energy from the wind or the sun. The knowledge simply isn't there, and, moreover, it isn't important. Who needs wind power when you can harness an atom, and the generators that do it work for well over a hundred years? Hard to argue with results like that; hard to care about anything else.