I guess there might be some issues from modern (ocean going) ship design that might also be worth considering. The 1st is that typically the electrical plant in a modern ship typically isn't really sized to carry the complete electrical load of everything onboard a ship.
Mostly this is due to the fact that you typically wouldn't be running some stuff at the same time (such as both compartment heating and the air conditioning). Similarly, some stuff (like the anchoring equipment) is used so infrequently that it wouldn't make sense to size the plant assuming that they would be running all the time.
Second, on most modern ocean going ships the electrical plant is composed of several smaller units/generators, so that you can take some generators offline when not needed, and/or for overhaul.
And finally, I believe that ships will have an emergeny generator, secifically to provide minimal services when the main plant is down.
It might be of interest to see how these type issues might ply out in Traveller terms, while not trying to get too overly complicatd.
For starters perhaps it could be assumed that there is a certain minimum sized plant (based on hull size) that could maybe meet all normal requirements of space flight. When normal long range sensors or typical self defense ype weapons are needed, perhaps this notional plant size would be capable of providing that power, assuming that maybe normal lights are dimmed and fresh water regeneration (or other life support items) is slowed, etc. Additionally,it may also be possible to more or less ignore stuff like airlock recycling and typical mooring actions, as these would be assumed to only occur either infrequently or at times when oher stuff might not be on line, etc.
If a ship is meant for certain special duties such as a warship with alot of weapons and/or sensors, or a large capacity passenger ship, then it may need to increase the size of its powerplant based on some sort of rating based on the type & number of weapons and sensors or number and passage-type of the passengers carried (eg, high-passage passengers on a ship above a certain nominal amount may raise your power requirements a bit more than say a similar number of other type passengers, etc).
Finally, if the powerplant were assumed to be made up of smaller generating units then it might be simple enough to just assume that the plant can either produce full-power, 3/4 power, 1/2 power, 1/4 power, or some notional very low number (say just enough to provide minimal life support, very low lighting, just tolerable temperatures, and emergency comms/a distress beacon, etc ) assuming that the plant includes a small emergency "generator" only for use in such instances.
As suh, fuel capacity requirements for typical merchant ships can be based on assumed fuel consumption, assuming a notional power requirement (presumably its full load) while transiting to/from the jump point, perhaps a different notional power requirement while in jump (or perhaps not?), and another notional power load while docked and/or on a planets surface (which could perhaps be varied whether the planets atmosphere is breathable or not, etc). If said ship has to fire its defensive weapons, while in transit it could just be assumed that life support and other services may be lowered to allow that.
For warships then though you may have to make oher assumptions.
When considering damage, you could investigate perhaps shutting down life support completely in some parts of the ship and/or alternating between the use of maneuver drives and the weapons or sensors each combat phase to meet the lower power avialable, or something like that.
Anyway, just some thoughts.
Regards
Pat