The invention provides a control method for output energy of a power supply device and a relevant controller. The power supply device comprises a switch and an induction component. The method comprises the following steps of: switching on the switch to increase the stored energy of the induction component; detecting induction current which passes through the induction component, to generate a current detection signal; approximately limiting a peak value of the induction current by using a provided limiting signal; and updating the limiting signal according to the peak value and induction average current corresponding to the current detection signal to make the peak value and the induction average current get close to a preset relation along with a switching period, wherein the preset relation ensures that the output energy output by the power supply device in one switching period is approximately a fixed value.