8.5 volt was when It was running a official ethernet shield which is a tad greedy. It was about 9.2 with just the arduino and 9.8 open circuit. It did 'pull' with load but perfectly OK to go through the onboard voltage regulator. It was an old charger with a transformer inside (that and a bridge rectifier and nothing else before I added the electrolytic).
I wouldn't make any assumptions about switch modes either, I have a few that originated with Netgear access points labelled 12v 1 amp (efficiency level IV 
) and light as a feather. They have the right plug and polarity for the arduino which is nice but they are the better part of 16 volts running a plain arduino. They pull a little with load but not as much as a linear. They are perfectly OK providing the 'other circuits' don't pull more than a few mA. Sticking your finger on the Arduino voltage regulator whilst its running is a good indicator, if it burns, you need less amps or volts or both....... 