Make sure you are measuring AC voltage, not DC. 33-34V AC sounds too high for a transformer rated 24V AC. Perhaps cheap multimeters have issues measuring AC accurately (as the AC measurement is supposed to the root mean squared value). In any case, if OSBo runs off it fine, it should be ok.
When you say ‘having difficulty getting my OSBo controller to run stably from AC power’, do you mean the WiFi is unstable (i.e. lose connection) or that OSBo is not powering up? If it’s WiFi, I am not completely surprised: I also occasionally have trouble getting WiFi to stay on. It works better when the controller is placed close to the WiFi router. I think BeagleBone Black is not as forgiving as Raspberry Pi in terms of powering WiFi dongle through its USB port. Adafruit’s BeagleBone tutorial (http://learn.adafruit.com/beaglebone/wifi) mentions repeatedly that it requires a beefy power supply. I suggest that you try to use a wired Ethernet cable first, and see if that makes the system more stable.