A server rack system including a plurality of power supply units, a monitoring circuit, a rack management controller (RMC), and a plurality of server nodes is provided. The monitoring circuit is for monitoring the power supply units. The RMC is for monitoring the power supply units. When the monitoring circuit and/or the RMC finds that at least one of the power supply units failed to output a normal voltage, an operation status of the server nodes is lowered or at least one of the server nodes is forcibly shut down.