Solar panels have only been practical out to missions to Mars or the asteroid belt at farthest. For any more distant mission, nuclear power has been the only feasible power source, in the form of RTGs at least. Spaceborne nuclear reactors have long been contemplated for providing much higher levels of power.
The mass of a Voyager RTG putting out 158W is about 38 kg (84lb). (It looks like Voyager used 3 of these RTGs.) Seems like they would be too heavy for your purpose.
It seems the Galileo RTGs were more powerful: 300 W in 56 kg (123 lb). This is still pretty heavy but maybe getting in there.
It's been a while since I worked the numbers, but I believe that humans regularly put out more power than that during daily activities. Assuming the exoskeleton was extremely efficient, it wouldn't really get you all that much advantage.
A cyclist working hard will put out 300ish watts, so, during daily activities, unless you are talking extremely short bursts like lifting/jumping, we put out much less. Store a good amount of power in some capacitor system and that would be enough to power an exoskeleton I bet.
