In recent years, the reliability and continuity of service of powertrains have become major challenges for electric vehicles to enter the mass market. Indeed, defects in powertrains lead to malfunctions in vehicles and reduce their performance compared to conventional vehicles. In this article, we focus on the DC/DC converter associated with the fuel cell in the powertrain. The latter must address the major issues facing fuel cell electric vehicle applications, namely: low mass and small volume, high energy efficiency, reduction of input current ripple, and reliability. This work then consisted of sizing and testing the fault-tolerant DC/DC converter structure selected for P to C vehicles. Algorithms for managing the degraded modes of this converter were developed and implemented experimentally. In this regard, the interaction between P to C and the DC/DC converter was studied. A theoretical simulation approach was used to carry out this work. This approach made it possible, under the most demanding conditions, to achieve very high efficiencies in steady state for both converters: 97.2% for the VS = 400V version and 95.5% for the VS = 200V version, powered respectively by input voltages of 400V and 200V. For input voltages in the lowest range, the efficiency is naturally lower. However, we are confident that this criterion (ƞ ≥ 96%) will be met over the nominal voltage range (between 300 and 600V). This demonstrator has validated the real benefits of a two-stage structure for applications with high input voltage variation, with each stage achieving efficiency in excess of 98%.