Hi gals and guys.
Just for the record: to change the power on state (remember on/off of a powerplug after a powerout) you have to change the value in the cluster setting of the powerplug device via ZHA integration:
Attribute value: PowerOnState.On (or Off, or LastState)
Set 0 in attribute value to turn it off after poweron
Set 1 in attribute value to turn it on after poweron
Set 2 in attribute value to turn it to the last on/off state after poweron