This paper proposes an output voltage regulation scheme for a fuel cell-based power source. The proposed methodology relies on the design of a dynamic backstepping average current-mode controller considering the combined fuel cell stack and boost converter model. Also, an external loop for voltage regulation using a proportional-integral action is added. Moreover, to improve the robustness of the current loop, a load estimator using immersion-invariance approach is designed. As a result, an adaptive backstepping controller ensuring asymptotic stability via a Lyapunov function is achieved. Finally, based on a 460-W testbench and a DSPACE platform, the closed-loop system performance is evaluated through experimental results. An appropriate output voltage regulation and robust behavior concerning to load variation and fuel cell stack unregulated dc output voltage are exhibited.