We present a synthesizing thermodynamic approach to modeling and power maximization in various energy converters, such as thermal, solar and chemical engines and fuel cells. Static and dynamical systems are investigated. Thermodynamic analyses lead to converters’ efficiencies in terms of propelling fluxes. Efficiency equations are applied to find maximum power points in static systems. These efficiency equations are also applied to determine maxima of integrated power (work) in dynamical systems, which work with upgrading and downgrading of a resource medium. While optimization of static systems requires using of differential calculus and Lagrange multipliers, dynamic optimization involves variational calculus and dynamic programming. In reacting mixtures balances of mass and energy are applied to derive power yield in terms of an active part of chemical affinity. Power maximization approach is finally applied for fuel cells treated as flow engines driven by fluxes of chemical reagents and electrochemical mechanism of electric current generation. The efficiency decrease is linked with thermodynamic and electrochemical irreversibilities expressed in terms of polarizations (activation, concentration and ohmic). Maximum power data provide bounds for SOFC energy generators, which are more exact and informative than reversible bounds for electrochemical transformation.