I have my energy up to 500, a bit excessive but I figured why not.
Sacrificing the gypsies does gives you a boost to energy capacity, though I did not do that because I tried to aim for at least semi-good playthrough.
The ranger quest line boosts your energy.
Joining the Sisters of Fertility and progressing boosts your energy, and it doesn't matter if you choose dominant or submissive.
Those are the main single shot larger quantity energy boosts, HOWEVER
This new thing, with the sandworm. If you agree to let it stay and keep the few girls that it has, and you come to be on "good terms" with it, you may willingly breed with it as many times as you like and every time you do this, you gain +5 to your energy capacity. You may repeat the process, however tedious, till you have as much energy as you want to have. Currently the quest is bugged if you try to walk out of the cave though. You get sent back towards the worm constantly, however the easy fix to that is to just use cheats to teleport to either Valos or Rathpike. I understand some people may not wish to use cheats at all but it is the simplest solution to leaving the cave in its current state.