Actually, I am not trying to save power but just to protect my router so that it won't go bad too soon.
However, after couple of trial and error, I succeeded in getting it to work the setup I wanted.
Basically, it was the sequence that I turned on those hardware making the difference.
It will not work if I turn on all the hardware at the same time. It will only work by turning the Modem power on first and let it run fully follow by the other two. If the modem did not run fully or to soon to turn on Obihai and router, it will not work either.