i don´t know (or remember) if this work in the original (disable other 
buildings to allow fortress to get energy), but is a good idea ;)

Under 50% hp the half of the guns disabled, when not enough power, the fortress 
simply disabled (if all fortress disabled, and no tanks the battle ll end)

yes, but i referred to the option of get off, disable energy of other building, 
to maintain energy in fortress to resist... this i don´t remember how work in 
the original game

In the original game there is a priority of how the buildings lose the power 
(stop working) when the enemy is destroying the power plants, or you just start 
to shut them down - try it, you'll see. The last are the fortresses.
When the power is out, they work just like they were damaged to 50%++, so one 
gun (tipically the stronger one, if the building has two different guns) is 
out. And of course the garthog fortress loses two guns.