The power supply powered the entire circuit, working with a transformer and rectifier to bring the mains voltage down to a more reasonable 12v DC.
Since someone brought this topic back, I might as well let everyone know what I discovered.
The motor was drawing WAY more current than I thought. I used to think that the lm317 would just turn off if I tried to draw too much current, when in reality it just limits the voltage at the output.
So when I hookup up the motor it worked fine for the first few seconds but slowly degraded in performance as the 317 lowered the output voltage to protect itself.