Use the /SP/policy HOST_AUTO_POWER_ON property to power on the host when external power is applied to the server. If this policy is set to enabled, the SP sets HOST_LAST_POWER_STATE to disabled.
-> set /SP/policy HOST_AUTO_POWER_ON=value
where value can be:
When power is applied, automatically powers on the server when the SP has been booted.
(Default) Keeps the server powered off when power is applied.