The power management system tracks the total amount of power drawn from a bus by devices connected to the bus and to the bus itself, based on the individual operational status of each device. The power manager system also tracks the total amount of power supplied to the bus. From this information the power manager system determines whether a power surplus exists sufficient to allow an additional device to operate or to allow a currently operating device to draw more power. Power usage requests received from devices connected to the bus are granted or denied by the power management system based on the determination of available power. The power management system additionally is capable of sequencing the use of several devices to allow the devices to each operate while maintaining the total power draw within an acceptable range. The system provides for efficient use of a limited amount of power to allow operation of more devices than conventionally allowed with a bus. The system also can activate power supply devices which are off-line via soft-power-on commands to increase the total amount of power available. The system is advantageously implemented with any bus system having devices drawing power from the bus from power supplies providing limited power.