Strictly speaking, the Macbook is under no obligation to provide more than 100 mA to a device that doesn't properly negotiate for it, which I don't get the sense the power dock has the capability to do.
In practice it does seem though that it can work with a good 5v-3.3v regulator on many computers . I will say that my personal experience with doing so is using a well designed switching regulator, which converts energy unlike a simple linear regulator - ie, the computer has to supply somewhat less current at 5v than the device is drawing at 3.3v.
Ultimately, power issues are the #1 cause of reboots (especially around the time of wifi startup) and all of ultimate power source, regulator, and cabling should be considered... I had a system I was ready to give up on, tried a different (and confusingly, much smaller physically) source and regulator, and it's been wonderfully stable since.
Looks like your connection to Onion Community was lost, please wait while we try to reconnect.