Passivity-based feedback controllers are derived for the indirect stabilization of the average output voltage in pulse-width-modulation (PWM) controlled DC-to-DC power converters of the ’boost’, ’buck-boost’, and ’buck’ types. The controller design is carried out on the basis of well-known average PWM models of such circuits. The average models are first shown to be Euler-Lagrange systems corresponding to a suitable set of average Euler-Lagrange parameters. The proposed regulators are based on an ’energy shaping plus damping injection’ scheme, achievable through nonlinear dynamical feedback. The performance of the proposed passivity-based duty ratio synthesis policies is tested for the ’boost’ converter case. The regulating feedback law, derived on the basis of a ’boost’ model composed of ideal switches and ideal circuit components, is assessed, via computer simulations, on a realistic stochastically perturbed switched converter model, including parasitic resistances and parasitic voltage sources.