Yes, your grandfather's transformer was onboard a plane. Check the 10.000 ft max label. When height increases, the air becomes thinner, and generators & electrical system starts to arcing, if not properly isolated.
Modern aircraft electrical system:
115 VAC, 400 Hz, motor driven generator(s)
28VDC, batteries
115VAC, 400 Hz, battery powered inverter, for emergency use only
There may be also a small turbine called APU, that generates electrical or phneumatic power to start the engines. Instead of APU, an external power supply may be attached, the ground power unit, to do the same.
If everything goes wrong in flight, a small "windmill" called the RAT (ram air turbine) is deployed to provide electrical power to drive the control surfaces on wings and tail