Adaptive regulation of pulse-width-modulation (PWM) controlled DC-to-DC power supplies is proposed using a suitable combination of dynamical input-output linearization and the ’backstepping’ controller design method. A nominal parameter, input-dependent, state coordinate transformation of the average PWM converter models leads to a type of pure parameter feedback canonical form associated with the Fliess generalized observability canonical form of such average models. A backstepping design procedure can then be immediately devised which leads to a dynamical adaptive regulation scheme for the generation of the stabilizing duty ratio function. The validity of the proposed approach, regarding control objectives and robustness with respect to unmodelled, yet unmatched, and bounded stochastic perturbation inputs, is tested through digital computer simulations.