This paper introduces a transformer-based converter suitable for high-voltage and high-power dc loads, e.g., electrostatic precipitators (ESPs). The proposed ESP supply has a rapid dynamic response in complex precipitation conditions with an improved hardware-based hysteresis current control system. The power level can automatically track the load fluctuation to guarantee the particle collection efficiency of precipitators. According to the relationship between switching frequency, current hysteresis width and output voltage, a quasi-constant operating frequency is achieved over the entire load range by dynamically adjusting the hysteresis width, which avoids excessive switching losses and voltage ripple. The system is co-designed with the medium-frequency transformer to optimize the loss and performance. The experimental results verify that the devised system is reasonable, reliable, and saves energy. The field operation data on pollutant emission satisfy the strictest standards in China and the European Union.