A comparison of two vehicle power-train topologies is performed for a small fuel cell andsupercapacitor powered delivery vehicle to determine the power-train weight and costtrade-off. The topologies use either a single DC-DC converter to interface the fuel cell,with the supercapacitors directly connected to the traction drive, or two convertersseparating both the fuel cell and supercapacitor from the traction drive. Energymanagement strategies are implemented to increase system efficiency at the expense ofincreased supercapacitor storage. The two converter system results in a lower cost and mass design due to a higherutilisation of the supercapacitor buffer. The energy management strategy can increaseefficiency, however, in this study the duty of the vehicle and the cost of hydrogen are lowresulting in a fuel saving that is outweighed by the additional hardware outlay. To interface supercapacitors and fuel cells with traction drives, efficient and compact DCDCconverters are required, therefore a dual-interleaved boost converter with interphasetransformer is designed and a volumetric and mass dense prototype is produced. Theconverter uses an inductor and interphase transformer which are potted in heat sinksbolted to a water cooled cold plate. Thermal finite element analysis and a MATLAB designprogram are used to determine the smallest thermally suitable inductor and interphasetransformer designs. The resulting prototype is superior in mass and volumetric powerdensity to commercial products, achieving 4.3 kW/kg and 7.2 kW/l including casing, usingoff-the-shelf components, and designed with a low part count. The anticipated nextgeneration converter will increase these power densities to 5.2 kW/kg and 9.2 kW/lthrough a modified layout and refined magnetic design.