A resonant power converter, comprising: a switch circuit, a resonant tank, a transformer, and a rectifier circuit connected sequentially, wherein the switch circuit is adapted to receive an input voltage (Vin) from an input source, and the rectifier circuit is adapted to output an output voltage (Vout) to a load; and a current synthesizing module, comprising: a sensing circuit configured to sense a resonant capacitor voltage (Vcr) on a resonant capacitor of the resonant tank; a peak hold circuit electrically connected to the sensing circuit for receiving the resonant capacitor voltage (Vcr), wherein the peak hold circuit is configured to acquire a peak value (Vcr_ph) of the resonant capacitor voltage (Vcr); and a calculation unit electrically connected to the peak hold circuit, wherein the calculation unit is configured to receive the peak value (Vcr_ph), a switching frequency (Fsw), the input voltage (Vin), the output voltage (Vout), and a resonant capacitance (Cr) of the resonant capacitor of the resonant power converter and generate a synthesized output current (lout) accordingly based on an equation: Iout = K ∗ Vin ∗ Fsw ∗ Cr ∗ 2 ∗ Vcr _ ph − Vin Vout where Iout is the synthesized output current, K is an efficiency coefficient, Vin is the input voltage, Fsw is the switching frequency, Cr is the resonant capacitance, Vcr_ph is the peak value, and Vout is the output voltage. a switch circuit, a resonant tank, a transformer, and a rectifier circuit connected sequentially, wherein the switch circuit is adapted to receive an input voltage (Vin) from an input source, and the rectifier circuit is adapted to output an output voltage (Vout) to a load; and a current synthesizing module, comprising: a sensing circuit configured to sense a resonant capacitor voltage (Vcr) on a resonant capacitor of the resonant tank; a peak hold circuit electrically connected to the sensing circuit for receiving the resonant capacitor voltage (Vcr), wherein the peak hold circuit is configured to acquire a peak value (Vcr_ph) of the resonant capacitor voltage (Vcr); and a calculation unit electrically connected to the peak hold circuit, wherein the calculation unit is configured to receive the peak value (Vcr_ph), a switching frequency (Fsw), the input voltage (Vin), the output voltage (Vout), and a resonant capacitance (Cr) of the resonant capacitor of the resonant power converter and generate a synthesized a sensing circuit configured to sense a resonant capacitor voltage (Vcr) on a resonant capacitor of the resonant tank; a peak hold circuit electrically connected to the sensing circuit for receiving the resonant capacitor voltage (Vcr), wherein the peak hold circuit is configured to acquire a peak value (Vcr_ph) of the resonant capacitor voltage (Vcr); and a calculation unit electrically connected to the peak hold circuit, wherein the calculation unit is configured to receive the peak value (Vcr_ph), a switching frequency (Fsw), the input voltage (Vin), the output voltage (Vout), and a resonant capacitance (Cr) of the resonant capacitor of the resonant power converter and generate a synthesized output current (lout) accordingly based on an equation: Iout = K ∗ Vin ∗ Fsw ∗ Cr ∗ 2 ∗ Vcr _ ph − Vin Vout where Iout is the synthesized output current, K is an efficiency coefficient, Vin is the input voltage, Fsw is the switching frequency, Cr is the resonant capacitance, Vcr_ph is the peak value, and Vout is the output voltage.