emergency power supply; backup power; emergency power source
vehicle-mounted electricity generator (e.g. for filming, emergencies, etc.); power-generating railway car (e.g. for air-conditioning on a non-electric train)
external power source; external power supply
power supply unit; PSU; power module
development of electrical power resources
loss of power; power outage; blackout
uninterruptible power supply; UPS
switched-mode power supply; switching regulator
power disconnected (state)