Sure, a smoke unit uses lots of power. That supply might even have trouble with just a smoke unit alone if it's 1.5a .
You're making less available for the motor, splitting whats there. Your smoke unit is likely weaker than it will be with more power as well.
The breaker shutting off is telling you that the draw is too high. It's either wire/track issues, or the loco draws more than max output.
An underpowered motor can get very hot without ever tripping a breaker. Always supply excess amps. Always avoid supplying excess voltage. (or too low, too near stall voltage)
It doesn't matter the scale or ac or dc, more amps supplied than used is a given. My advice is always buy plenty of amps (and close match volt range) the largest you can manage really. That way you are always covered for bigger, better, and just plain more.
