yes, you would need a somewhat expensive to an expensive meter to measure the AC at true RMS. Look for a used Fluke if you must have one.
You don't want to exceed 20 volts AC on the track for Lionel products.
I would measure the voltage at the receptacle. That may be a little high. I don't have any 180 watt bricks that exceed the 18 volt plus or minus a small fraction.
I agree with PLCPROF, it's ok. Enjoy your trains.