Airports utilize two separate forms of power supplies.
In order for an aircraft to power up, a ground power unit is typically built into the jetway for easy accessibility. These units are capable of handling high amounts of voltage when connected to a separate generator making them the ideal power source for an aircraft.
Typically, the aircraft would generate its own power, but when it’s parked, this unit becomes the main power source once the engines have turned off. There are separate types of ground power that are available on the jetways: fixed ground power and mobile power.
Fixed Ground Power
Fixed units are permanent establishments that are installed where the aircraft is parked. They operate at a 400 Hz power line which is transferred by either a centralized system or by point of use through multiple frequency converters. A centralized system is convenient in that a central location stores a high rate of power, which is then distributed to each aircraft at a set rate. The other option, point of use, takes the central power unit close to the aircraft and then converts it to the proper amount of Hz.
If there are no fixed ground units established, then mobile power units are dispatched to supply the aircraft with power. These tend to be hauled by another vehicle and placed in a specifically designated area close to the aircraft. Many times diesel generators are hooked onto the portable power unit, which then converts the energy into the proper amount that is needed.
Also, you’ll find that larger aircrafts will require more than one portable power supply in order for it to be adequately charged. This is common and if you look out of the terminal window, you’ll most likely see the larger crafts being tended to by multiple units at once.