That's an interesting question. According to Rich and Greg's Airplane Page[1], the A320 has three generators rated for 90kVA continuous each, one per engine and a third in the auxilary power unit that isn't normally deployed. Cruising demand is around 140 kVA of the 180 kVA supplied by the engines, leaving 40 kVA to spare. The A380 has six similar generators, two in reserve. They give the percentages so you could calculate how much fuel each system is consuming.
[1] https://alverstokeaviation.blogspot.com/2016/03/
This page also has a rendered image of the generator:
https://aviation.stackexchange.com/questions/43490/how-much-...