A server rack system includes a plurality of servers, a plurality of power supply units for supplying power to the servers, and a microcontroller electrically connected to the servers and the power supply units. The microcontroller is configured to determine a number of those of the servers that are currently in operation, compare the number with a critical value, determine whether each of the power supply units operates normally, and control at least one of the servers that are currently in operation to operate at a lower operating frequency when the number is greater than the critical value and at least one of the power supply units operates abnormally.