I believe a switched mode 12V power supply would work with the smart plug too, the power supply I got probably would work but it takes a while to discharge so the voltage drops enough to shut the amp off. I never left it on long enough to find out.
Since the Micromega M-100 Trigger In can accept 5v to 12v, if in the future your source does not offer a trigger output option, my suggestion would be to use a 5V or 6V supply instead of the 12V supply, which will significantly reduce its discharge time.