An airplane ground support system includes a multi-voltage power supply. A control system within the power conversion module receives measurements to regulate the power module's output to a predetermined preset voltage level as mandated by the power output selection signal. In an alternate embodiment a multi-voltage or upgradable power supply has A.C. and D.C. capability, A.C. only capability with an upgrade kit available to add D.C. capability in addition to the A.C. capability, D.C. only capability with an upgrade kit available to add A.C. capability in addition to the D.C. capability.