Some questions on batteries and AC power for lego

[CP5670]

I posted this on lugnet but didn't get any response, so I figured I would try here too. :-P

There seems to be a difference between the voltage outputs of battery boxes and wall powered sources like the train speed regulators. From just listening to the sounds that motors make, a battery box puts out the same voltage as a speed regulator on the second to last setting, but the regulator on maximum speed runs motors a bit faster than anything a battery box can do, even on a fresh new set of (alkaline) batteries. I have one of the newer control centers (with an AC jack) which also runs motors at the faster speed, and similar comments apply to light pieces which look brighter. Do the Lego wall powered sources actually output slightly more than 9V? The Lego AC adapters are labeled as having 12V output, and the control center