Controlling server power usage in a data center is provided. Power usage among a plurality of server racks in active mode processing a set of workloads in the data center is managed. It is detected that a new server rack in standby mode is being added to the plurality of server racks. It is ensured that the new server rack in the standby mode is properly controlled and monitored prior to transitioning the new server rack to the active mode. It is determined whether power safety criteria are met to safely join the new server rack to the plurality of server racks prior to transitioning the new server rack from the standby mode to the active mode. The new server rack is transitioned to the active mode in without exceeding a power budget for the plurality of server racks in response to determining that the power safety criteria are met.