Interface circuitry of a storage device or other type of processing device comprises at least one data path, and an adaptive power supply configured to provide a variable supply voltage to the data path. The adaptive power supply comprises a reference voltage circuit having a plurality of field effect transistors collectively configured to provide a variable reference voltage, with different ones of the field effect transistors being biased into different operating regions. For example, a first subset of the field effect transistors may each be biased into a linear region such that the variable reference voltage tracks variations in on-resistance of one or more corresponding field effect transistors of the data path, and a second subset of the field effect transistors may each be biased into a saturation region such that the variable reference voltage tracks variations in threshold voltage of the corresponding field effect transistors of the data path.