A server rack system includes a rack, a power transmission module, a power supply module, and operating units. The power transmission module configured at the rack includes first, second, and third conductive pillars. When the power supply module slidably configured in the rack is completely installed in the rack, the power supply module electrically connects the first, second, and third conductive pillars to receive high-voltage direct-current (DC) electric power through the first conductive pillar electrically connecting an external power supply. When the operating units slidably configured in the rack are completely installed in the rack, the operating units electrically connect the second and third conductive pillars. The completely installed operating units transmit signals indicating the complete installation to the power supply module, such that the power supply module converts the high-voltage DC electric power into low-voltage DC electric power and transmits the low-voltage DC electric power to the operating units.