This is a common problem, old "power hungry" HomePlug adapters used to be on all the time so were fine. What happens is that the adapter doesn't wake up quickly enough to service the initial DHCP requests for the unit to obtain its IP address from the router - nothing to do with Ethernet power, it's just traffic!
I know how this works on an HD-FOX or HDR-FOX, I presume the Foxsat is similar. The way to solve the problem (on HD/HDR-FOX) is to go into the Internet Setting menu, and (with DHCP selected) click "Apply". The HomePlug should be awake and will pass the request on to the router. Having then established your IP settings, change from DHCP to manual.
You should then act to configure the router properly for this, but you will probably be OK without bothering. I will add a reference to more info later.