A converter includes an input capacitor, a primary-side switch circuit, a transformer, an inductor, a secondary-side switch circuit, and an output capacitor. The primary-side switch circuit includes a first and a second bridge arm. Each of the first and the second bridge arm includes at least two switches. A soft-start period of an output voltage from the converter includes a voltage rising period of the output voltage. A turn-on time of one of the at least two switches of the first bridge arm is less than ½ of a switching period. A turn-on time of one of the at least two switches of the second bridge arm is zero of the switching period or near zero of the switching period. The inductor and parasitic capacitors of the at least two switches of the second bridge arm oscillate, and energy generated from an oscillation is transmitted to the second-side switch circuit.