We develop in this paper an adaptive passivity-based controller for output voltage regulation of DC–DC buck–boost converter with an unknown constant power load. This control problem is theoretically challenging since the average model of the converter is a bilinear second order system that, due to the presence of the constant power load, is non-minimum phase with respect to both states. A solution to the problem was recently reported in Wei et al. (2017), however, the resulting control law is extremely complicated to be of practical interest. The purpose of this paper is to present a new, significantly simpler, controller that can be easily implemented in applications. The key modifications introduced in the new design are the use of a change of coordinates and a partial linearization that transform the system into a cascade form, to which an adaptive energy-shaping controller is applied. Another advantage of the proposed controller, besides its simplicity, is that it is amenable for the addition of an outer-loop PI that improves its transient and disturbance rejection performances. Simulations and experimental results are provided to assess the improved performance of the proposed controller.