The Westland Sea King normally has two AC generators installed on the accessory part of the main gearbox. It is possible that some mark numbers has three generators as it is room for it.
Because of an actuated free wheeling unit on engine no 1 it is possible to drive only the accessory part of the MGB without turning the rotor. This will give you hydraulic power and AC power.
All DC power is provided by two TRU (transformer and rectifier unit) or the battery.
There is also a ground inverter, converting 28 VDC to 28 VAC for some instruments.
You will have under frequency protection on the ground only (around 94%).
This how it is on our Sea Kings, but i dont think there is going to be a big difference to other mark numbers.