OK, you may not realize the smoke will draw at least an amp itself? With the motor, smoke unit and a few LEDs you are
over the design current of your NCEsystem.
Also, the Aristo smoke unit uses a switching power supply, so will draw more current at lower voltages.
If you want good smoke, you need to budget 1 amp best case for your fan driven smoke unit, and I'm referring to your opening post, where the goal was a lot of smoke.
I would suggest a few things in your setup:
1. buy a 5 amp booster from Tam Valley
2. buy an inexpensive 5 amp, 18 volt regulated DC power supply (laptop, cheap on ebay or Amazon).
Now you have 5 amps and about 18 volts DCC to the rails, you will not be overheating your PowerCab, and your G scale locos will run much better and you won't be starving for amps or volts.
For the loco, put a relay (with snubbing diode) on the function output of the decoder, and switch track voltage to the smoke unit with the relay.
This will work very well.
Greg
p.s. here is a link to a small portable system based on the powercab with the 5 amp booster.
Greg Elmassian web site on large scale trains and garden railroads, cigars, and computers
elmassian.com