Modeling and simulation are powerful tools to design power distribution systems made up by multiple converters and loads, such as the system of the more-electric-aircraft. However, the system designer usually has no access to detailed data of the power converters, due to confidentiality of manufacturers. Therefore, a behavioral black-box modeling approach is necessary. These models can be used to evaluate the response of power electronics systems which are composed of commercial converters, since they can be fully parameterized from the actual converter response and only reproduce the signals required for a system-level analysis: input-output voltage and currents. Moreover, they do not reflect internal data of the converter, so the confidentiality of the manufacturer is kept.In this paper a black-box modeling method of DC-DC converters, based on time domain measurements, is proposed. This method is based on the analysis of the step transient response, which is obtained by means of simple experiments. The identification of the model is carried out by using well established fitting algorithms, which can be applied using commercial tools. Experimental results obtained on a commercial DC-DC converter are shown in order to validate and to illustrate the proposed method.