A load adaptive power supply including: a conducting resistance controllable bridge rectifying unit for generating a full-wave rectified output voltage according to an AC input voltage to drive a load, and controlling an on-resistance thereof during at least one half cycle of a positive half cycle and a negative half cycle of the AC input voltage according to at least one control signal; a driving circuit unit configured to generate the at least one control signal according to a pulse modulation signal; and a digital microcontroller unit coupled with the driving circuit unit to determine a duty ratio of the pulse modulation signal according to a power of the load to drive the driving circuit unit, so as to adjust the on-resistance of the conducting resistance controllable bridge rectifying unit according to different values of the power, thereby increasing a power conversion efficiency of the power supply.