For high power density and high power efficiency, resonant converter-based power supplies are preferred for high-power applications. This paper presents a resonant power supply for an indigenous 400 A/120 V DC plasma torch. At 400 A, the size of the magnetic components, i.e., inductors and transformers, is cumbersome in their fabrication, testing, and maintenance. So, a modular approach is adopted with three parallel modules each carrying one-third of the total load current. The proposed design has several advantages including high performance, rapid production, ease of testing, and reasonable manufacturing costs. Detailed calculations of the proposed design are presented and compared with a design based on a single module. The prototype is evaluated in simulations incorporating a dynamic model of the load. The simulations’ results have proven the validity of the proposed design. Moreover, hardware implementation of a single module of 135 A/120 V is accomplished and tested at full load. The work presented in this study has laid a strong foundation for the indigenous fabrication of the power supply for the plasma torch.