Also, source power (amps) is more important than potential (volts),
Amps are important but amps and voltage work together. In simple terms, voltage is speed and amps are power. Any major DCC system you can buy today will have enough power to move at least one S scale locomotive. The Lenz 100 is a 5 amp system aimed at S and O scales.
Use a DCC meter under load (~1.5A with a light bulb) to measure DCC voltage to the rails as you drag it along your tracks.
Good idea. While it is true that a standard meter doesn't report the actual DCC voltage, the reading given is still useful for comparisons around the layout.