More voltage than supplied
If your power supply is an unregulated linear type then the unloaded voltage will be higher than its rating. Depending on what it was it was designed to power it may not have a filter capacitor either, in which case the peak voltage will be higher that the average that your meter shows.



When a motor is running it also acts a generator, producing a voltage which is slightly less than the driving voltage. When powered from unfiltered rectified AC it will 'fill in the gaps' between the peaks, and raise the average voltage.  

I ran a small 6V motor on rectified AC and the voltage shown on the meter rose by 35% (from 4.4V to 5.9V). In the oscilloscope trace below you can see a high frequency waveform which is the voltage generated by the motor, and two 'bumps' which are the rectified AC from the power supply. Without the motor connected those bumps go down to zero volts.