This presentation is on an alternative power delivery architecture for data center servers that can achieve much higher energy efficiency than conventional architectures. Contemporary architectures consist of cascaded power conversion stages, with each stage processing the full server power. The series-stacked power delivery architecture has been proposed recently, where servers are connected in series, and only the mismatch in the servers’ power is processed by power converters. Since only a small portion of the full server power is processed, the power loss can be significantly reduced, resulting in extremely high efficiency. This architecture is validated experimentally with four GaN-based 4-to-1 DC-DC converters, and up to 99.2% power conversion efficiency is achieved.