An aircraft device power supply adapted to be connected to either an aircraft alternating current power bus or to an aircraft direct current power bus, and comprising: a first subcircuit having an input and an output (418H, 418L), the first subcircuit configured to accept an AC power signal, convert the AC power signal to a lower voltage which is approximately equal in magnitude to a voltage supplied by the aircraft's DC power bus, and output a lower voltage rectified AC power signal, when the power supply is connected to an aircraft AC power bus; an AC/DC switchover subcircuit (120, 120a, 120b) having a first input connected to the output (418H,418L) of the first subcircuit and a second input (520H, 520L), and further having a switchover output (428H, 428L) to which the first input (418H, 418L) and the second input both are connected, the AC/DC switchover subcircuit (120, 120a, 120b) configured to: output the lower voltage rectified AC power signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft AC power bus and not to an aircraft DC power bus; and output a DC signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft DC power bus and not to the aircraft AC power bus; a power factor correction subcircuit having an input connected to the switchover output (428H, 428L), and further having an output (126H, 128L), the power factor correction subcircuit configured to correct a power factor of a lower voltage rectified AC power signal, when the power supply is connected to the aircraft AC power bus, and further configured to output a DC power signal having a first voltage; and a DC-DC step-down converter having an input connected to the output (126H, 128L) of the power factor correction subcircuit, and further having a system voltage output, the DC-DC step-down converter configured to reduce the first voltage to a second voltage lower than said first voltage. a first subcircuit having an input and an output (418H, 418L), the first subcircuit configured to accept an AC power signal, convert the AC power signal to a lower voltage which is approximately equal in magnitude to a voltage supplied by the aircraft's DC power bus, and output a lower voltage rectified AC power signal, when the power supply is connected to an aircraft AC power bus; an AC/DC switchover subcircuit (120, 120a, 120b) having a first input connected to the output (418H,418L) of the first subcircuit and a second input (520H, 520L), and further having a switchover output (428H, 428L) to which the first input (418H, 418L) and the second input both are connected, the AC/DC switchover subcircuit (120, 120a, 120b) configured to: output the lower voltage rectified AC power signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft AC power bus and not to an aircraft DC power bus; and output a DC signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft DC power bus and not to the aircraft AC power bus; output the lower voltage rectified AC power signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft AC power bus and not to an aircraft DC power bus; and output a DC signal at the switchover output (428H, 428L), when the power supply is connected to the aircraft DC power bus and not to the aircraft AC power bus; a power factor correction subcircuit having an input connected to the switchover output (428H, 428L), and further having an output (126H, 128L), the power factor correction subcircuit configured to correct a power factor of a lower voltage rectified AC power signal, when the power supply is connected to the aircraft AC power bus, and further configured to output a DC power signal having a first voltage; and a DC-DC step-down converter having an input connected to the output (126H, 128L) of the power factor correction subcircuit, and further having a system voltage output, the DC-DC step-down converter configured to reduce the first voltage to a second voltage lower than said first voltage.