High performance cloud computing enables manykey future technologies such as artificial intelligence (AI), selfdriving vehicle, big data analysis, and the internet of things (IoT),using clustered CPU and GPU servers in the datacenter. Toimprove the power efficiency and the infrastructure flexibility,the computing industry is adopting 54VDC to power the serversin the open compute racks. In this paper, a new modelingtechnique for a soft-switched DC-DC converter is presented andsuitable to guide optimal design in different applications, forexample, 54V to point-of-load (PoL) for the new open computerack. To improve the model accuracy and reduce the complexity,this paper proposes a reduced order linear differential equation(LDE) based modeling technique to discover 1) the tankresonance involving the output inductor; 2) output current rippleand its impact on power efficiency; 3) the proper on-time controlfor soft switching; 4) unique bleeding mode under the heavy load;5) output power capability of the converter; and 6) componenttolerance analysis and impact on the performance of theconverter. With the power loss estimation, design guideline isprovided for a reference design and design improvement basedon this new modeling technique. Using the proposed method,great accuracy can be expected in the efficiency estimation.Simulation and experimental results are provided to verify themodeling technique in a 54V-1.2V 25A DC-DC converterprototype.