This paper presents the prototype development and performance evaluation of a three-stage flyback-based Input Series Converter designed as an Auxiliary Power Supply (APS) for a Modular Multilevel Converter (MMC)-based Arbitrary Waveform Generator (AWG). The APS is connected across the submodule capacitors of the MMC and converts the capacitor voltage to 24V, providing power to the gate drivers and control units within each submodule. The proposed converter features integrated active Input Voltage Sharing (IVS), a scalable architecture, and wide-input voltage operation. A multi-winding flyback transformer ensures high-voltage insulation between the submodule capacitor and the APS output while facilitating active IVS for balancing input capacitor voltages. A transformer prototype has been developed and tested in an open-loop converter configuration. The system’s performance has been evaluated at an output power of 30W across an input voltage range of 300V–3600V.