The problem of high voltage spikes, generated at the switch-offinstant in a hybrid DC converter based on switched capacitors and a high-frequency transformer, is addressed by introducing a primary-side clamping circuit. Passive clamping circuits are utilized for their simple design, low cost, and effectiveness in suppressing voltage spikes. Three passive clamping circuits-resistor-capacitor-diode, inductor-capacitor-diode and an energy feedback circuit—were selected to absorb leakage inductance energy. At the moment of switch-off, a new current path was formed to absorb and transfer this energy, limiting the voltage spike and ultimately reducing the voltage stress on the switching device. Detailed designs of the three circuits were first presented, followed by a comparative analysis of their spike suppression effects and efficiency. Finally, an experimental prototype with specifications of 36.3~69.5 V input, 400 V output, and 50~150 W power was designed and fabricated. The spike suppression performance and efficiency of the three circuits were then experimentally compared and verified. The results demonstrate that each clamping circuit offers distinct advantages, allowing for selection based on the specific application requirements of the hybrid converter.