As major web and cloud service providers continue to accelerate the demand for new data center capacity worldwide, the importance of power oversubscription as a lever to reduce provisioning costs has never been greater. Building on insights from Google-scale deployments, we design and deploy a new architecture across hardware and software to improve power oversubscription significantly. Our design includes (1) a new \em medium voltage power plane to enable larger power sharing domains (across tens of MW of equipment) and (2) a \em scalable, fast, and robust power capping service coordinating multiple priorities of workload on every node. Over several years of production deployment, our co-design has enabled \em power oversubscription of 25% or higher, saving hundreds of millions of dollars of data center costs, while preserving the desired availability and performance of all workloads.