A power supply unit adapts based on an image to be displayed by a display panel. The power supply unit includes a controller circuit for generating a control signal, and a converter circuit for generating an output supply voltage based on the control signal. The controller circuit includes a first look-up table (LUT) storing a set of lower limit values, and a second LUT storing a set of upper limit values. Moreover, the controller circuit includes a microcontroller for receiving an on-pixel-ratio (OPR) value and identifying an entry in the first LUT and the second LUT from the received OPR value. The controller circuit further includes an output circuit for generating the control signal between a first voltage corresponding to a lower limit stored in the identified entry in the first LUT and a second voltage corresponding to an upper limit stored in the identified entry in the second LUT.