Is it smart to use a 12vDC / 2A regulated power supply for an Arduino Uno?
I have heard that the voltage regulator on the Arduino may overheat.
It depends on how much power is drawn through the regulator.
Therefore I beleive the arduino is only using 5v to power the max 7219 and small amps to open the source drive outputs. Everything is working GREAT right now. But I am finalizing the project and want to only have one power source to my project. I have been powering the Arduino by USB until this point. I do want to utilize the 12v/dc regulated power to power the Arduino.
If that's everything
then you're only drawing about 50mA of current and you should be fine.
PS: A simple test is to put your finger on the regulator...if you say "ow!" then you need to reduce the load.