The power draw of equipment in a data center may be capped in order to keep the power draw under the capacity of the Uninterruptable Power Supply (UPS) that serves the data center. The current capacity of the UPS may be estimated, and the equipment may be controlled so as to keep the equipment's power draw under that current capacity. Factors that may affect the estimate of the UPS's current capacity include the history of temperature and humidity to which the UPS has been subject, and charge/discharge history of the UPS. Factors that may affect the decision of which equipment to throttle to a lower power level include: the current power load at the data center, the type of software that each server is running, and the demand for that software.