Analytical description of a constant power fed supercapacitor behavior is revealed in the paper. The derivation is based on a simple RC model with parameters taken from a manufacturer datasheet. Different power and energy-related figures of merit are obtained using the derived expressions. It is shown that some of the performance figures used in datasheets are strictly theoretical and cannot be achieved in practice. The process of Ragone plot construction based on the proposed method is described as well. Moreover, it is shown that the upper limit of a supercapacitor voltage imposes certain limits on power and energy capabilities of the device. Extended simulation and experimental results are provided in order to reinforce the proposed method and justify the selected model for describing supercapacitor performance. Appropriate comparison of simulations and experiments shows that the simple first-order model may be utilized to predict supercapacitor behavior with reasonable accuracy to perform an initial design.