Where does capacity come from?

When a Coolidge tube is operated for some time it becomes hot. Where does the heat come from?

If the nucleons of a nucleus are separated from each other, the total mass is increased. Where does this mass come from?

When a ferromagnetic material goes through a hysteresis loop, its theremal energy is increased. Where does this energy come from?

When you push your bicycle up on an incline the potential energy of the bicycle and yourself increses. Where does this energy come from?