any decent 12Vdc power supplies that can be used as a 12V trigger?

Are you asking about +12V trigger for power supply sequencing?  If so, devices have their own internal pull-up to 12V and are being shut down by pulling it down to GND.  I had one power amp that required more current to pull to GND than pre was able to deliver and had to put Normally Closed optical switch in series.

I have a Micromega M-100 and I want to use a 12Vdc power supply plugged into a smart plug so I can use as a sleep timer. The Micromega has a 12V trigger 

I believe that your integrated should work without anything connected - it pulls up trigger input internally.  In order to shut amp down you need to short this input to GND (or at least to drop voltage below 5V).  likely you don't need any external voltage.

From my understanding, The Micromega M-100 has a 12V trigger input, I need a 12V source to trigger it. I was going to plug a 12V power supply into a smart plug and control it with Alexa ( So I'd have a sleep timer )

Your amp will work, even without anything connected to trigger input.  Yes, amp turns ON with the presence of +12V, but this voltage is already there (pulled-up internally to 12V).  Try shorting this input to GND - it will turn your amp OFF while removing short will turn it back ON.  All you need is switch.

 

I just discovered my WiiM pro has a 12V trigger, going to try a cable from WiiM to amp.

I also discovered by e-mailing Micromega, Thier triggers are labeled backward due to a manufacturing issue, so I was plugged in to the output instead of the input. Waiting on my 2.5mm to 3.5mm trigger cable to come in tomorrow so I can try it with the WiiM Pro.

Got the cord for the WiiM pro from Amazon and it works great. 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.