There are two "outputs" on the board. The right hand side is the 'high' voltage side. This is the power coming straight from the DC jack or terminal block. There is a diode to prevent negative voltages but pretty much its going to be within 200mV of the input.
The left hand side is the 'regulated' voltage side. This is the power that is running through the voltage regulator. This voltage is adjustable
If you select 3.3v on the voltage selection switch you will be able to measure that output voltage. The red indicator LED will be somewhat dim