A track maintenance machine includes a machine frame being movable on a track, a plurality of working units, and a combustion engine to be connected by a clutch to a transfer case. Hydraulic pumps for supplying a plurality of hydraulic drives of a hydraulic system are connected to the transfer case. An electric motor is provided as an alternative drive of the transfer case for permanent energy supply of the working units and drives. The electric motor is coupled to an intermediate circuit to be supplied with electric energy by a vertically adjustable pantograph to be applied to a catenary of the track. A generator or an electric energy storage device is provided for alternative energy supply of the intermediate circuit. A method for operation of an energy supply system is also provided.