A method of optimizing a gain adjustment value Kadj for a digital controller in an isolated switched mode power supply. The power supply includes an opto-coupler having a current transfer ratio (CTRX) within a range defined by a minimum current transfer ratio (CTRMIN) and a maximum current transfer ratio (CTRMAX). The method includes determining the CTRX of the opto-coupler, determining an optimal gain adjustment value KadjX based on the determined CTRX of the opto-coupler, and storing the optimal gain adjustment value KadjX in the digital controller. The method can be performed by the digital controller or by a programming device external to the power supply.