What types of power do electric ground power units supply?

• A. DC power
• B. AC power
• C. DC and AC power
• D. Battery power

Answer: (C)

The essential idea is that an external ground power unit must be able to power the aircraft’s electrical system in both forms: AC and DC. Aircraft systems use AC power (often 400 Hz) for most equipment and loads, while DC power is used for battery charging, starting, and DC buses. A ground power unit can provide AC to feed the aircraft’s AC buses and DC to feed the DC buses and charge the battery, and many units are capable of delivering both at the same time. That’s why “both DC and AC power” is the best answer.

Providing only DC or only AC would not cover the full needs of the aircraft’s electrical system, and “battery power” describes an internal energy source rather than external ground power supplied by a GPU.