I am using an arduino UNO to run 2 stepper motors. Stepper motor - NEMA-17 size - 200 steps/rev, 12V 350mA : ID 324 : $14.00 : Adafruit Industries, Unique & fun DIY electronics and kits using the easydriver motor shield. https://www.sparkfun.com/products/retired/10267
What current should my power supply have? The motor specs say 350ma but the motor shield says 740ma. Can anyone help me with this?
The motor is rated for 350 mA maximum per winding and there are two windings. Unless you use the current limiting feature of the motor driver, you need 700 mA per motor, so the power supply should be capable of supplying more than 1.5 amperes. Of course, you will need two motor drivers.
There will be no problem if your power supply is capable of providing more current than you need - the motors will only take what they need.
You should also be aware that the current-rating for stepper drivers is normally specified on a per-coil basis. In other words the Easydriver can supply almost twice as much current as your motor requires. Be sure to set the current limit to suit your motor.
Have a look at stepper motor basics
...R