The Host.PowerState enumerated type defines the power states of a host.
POWERED_ON : The host is powered on. A host that is entering standby mode is also in this state.
POWERED_OFF : The host was specifically powered off by the user through vCenter server. This state is not a cetain state, because after vCenter server issues the command to power off the host, the host might crash, or kill all the processes but fail to power off.
STANDBY : The host was specifically put in standby mode, either explicitly by the user, or automatically by DPM. This state is not a cetain state, because after VirtualCenter issues the command to put the host in standby state, the host might crash, or kill all the processes but fail to enter standby mode. A host that is exiting standby mode is also in this state.
Enumeration: POWERED_ON, POWERED_OFF, STANDBY,