The server has two power modes: standby and full power.
The server enters standby power mode automatically when it is connected to AC power. This provides power for the SP. See How to Apply Standby Power for Initial Service Processor Configuration.
Full power mode is the normal operating mode. When the server enters full power mode, power is supplied to all system components, the server boots, and the operating system (OS) functions. See How to Power On All Server Components.
When you power off the server, it transitions from full power mode to standby power mode. See How to Power Off the Server.