We are talking about steppers here. So both does not apply to those motors.
Where did you read that? A UNO is not a power supply, and it cannot deliver more than maybe some leds need.
In any case you need a separate power supply for your motors.
The Motor shield Rev3 is not suitable for your steppers. It can only drive DC-motors or high voltage steppers. All of your steppers need current controlling stepper drivers, which are able to provide the rated current of the steppers. The power source should be at least a 12V power source. The upper limit depends on your selected drivers. To select the PSU, you must add all the power your steppers need (NOT the amperage!).