The Vcc of the Digital Breakout Board can be set to either +5V or +3.3V depending on the Vcc select jumper position.
The +5V output is associated with Pin 19 of the Digital Input connector of the RT Box. If you look at the Digital Input Connector pinout table in the RT Box manual, you'll see the rating of the output of 5V and 1.5A max.
For the +3.3V output connection there is a small onboard buck converter that steps down the +5V output from the RT Box. The current rating of the +5V input is limiting.