Multilevel converters are one of the major choices for realizing high electric power conversion. The major feature of multilevel converter topologies is the need for a large number of switches, each of which requires a gate driver circuit and an isolated DC power supply. In this paper, a pragmatic concept of design and implementation of an isolated DC-to-DC converter for a high-voltage isolated application is introduced. More specifically, a multiple isolated output power supply based on the benefits of resonant converters is designed to prepare 36 double DC voltages for driving power semiconductor devices in a three-phase, seven-level cascaded H-bridge that acts as a static synchronous series compensator (SSSC). The power supply contains several high-frequency transformers in series, carrying a high-frequency single turn current as their primary winding excitations, and they are improved by a resonant tank circuit to reduce switching and core losses. The proposed design has a high voltage insulation level, low cost, small size, adequate hold-up time, and an easily upwards extending structure. The feasibility of the design is clarified by simulation results and implementation in a high-power D-SSSC converter.