In order to better meet the charging demand of pulse adders with series core structure, a compact full bridge LLC converter charging source with high switching frequency was designed, and a method of additional balancing winding was proposed to improve the inconsistent charging voltage of each stage storage capacitor. After describing and analyzing the structure design, working process, and parameter design of the converter, an experimental platform for a 10-stage pulse adder and a resonant converter charging source was built. The experimental results show that, the soft-switching function is realized when the switching frequency is 100 kHz and the charging voltage consistency of each stage capacitor can be effectively improved by adding balanced windings. In addition, by adjusting the charging voltage of the converter charging source, the pulse adder can output 8 kV high-voltage pulses with a pulse width of 2 μs and a frequency of 10 kHz, which can meet the charging demand of the pulse adder.