Hi,
Depends on which engines that you are running - MTH or Lionel?
Also, that meter is only a visual reference - you should check you voltage at the track with a meter that measures in RMS voltages.
What is the load on the track when you took the photo? What needs 3 amps? Also, that amperage is the total of the tracks measured on the return or the U - not just one output - the late Dale Manquen documented this some time ago.
Those voltages on a non-RMS meter are most likely 18 volts coming from the bricks (PH-180)