The Etherdongle is powered with a Triad WDU6-600 wallwart. Nominally, this is a 6V DC 600mA brick. Open circuit (ie, not plugged into the ed, so no load) voltage is 9.4V. Given that it has a 7805 regulator, it needs to be over 7v under load. I measured mine and it's 7.3v (ed only, no conductor).
I would NOT feed in much more than 9v since any higher voltage results in more heat being generated in the regulator.
/mike