When a server enters a standby mode, electronic components in the server still draw power. A power supply is an example of one such component.
Current power supply designs operate all power supplies in a standby state while the server is in a standby state. Each power supply consumes a constant amount of power to be functional in addition to power conversion losses associated with the standby load.
If a server has multiple power supplies, then each of these power supplies continues to draw power and increase the costs associated with running the server even while the server is in a sleep or standby mode. Such costs accrue over time and can be substantial, especially in a data center that houses hundreds or thousands of servers.