@redcore If the motor driver are set correctly, they will require 1.5A so you have 1A max for the laser. A 2.5W needs nearly 1A at start up, so you are just within the limits of the power supply - if everything is set correctly.
If the motor drivers are set to 1A each then you are in trouble of course. They're 2A stepper drivers but 1A is the recommended max without a heat sink and fan.
Do you have a larger 12V power supply? 5A would be ideal for a test.