Rc car, power supply instead of alkaline battery?
In my experience, AA batteries fairly well never have a capacity >2.7Ah (usually 1.8-2.3Ah), so as long as your pack of series-connected AAs lasts >1hr in use, then you're for sure safe.

EDIT: At very worst, the 12V/2A power supply might yield a small reduction in initial power vs. the batteries, but should for most purposes be sufficient.