Wawa:
Some DMMs display a higher voltage if the battery goes flat.
Do you have a low battery warning on the LCD?
The Due uses a switching (buck) 5volt supply when on external power.
Seems a bad idea to power a DAC from a potentially dirty supply.
Make sure the DAC doesn't mind the 3.3volt logic.
Leo..
The DMMs is normal. I measured the 3.3V pin; it is always 3.3V.
I actually need a 5V range Analog signal. I am using this DAC: Overview | MCP4725 12-Bit DAC Tutorial | Adafruit Learning System