On Monday, November 23, 2020 at 3:50:47 PM UTC-5, Chuck wrote:
Well, I have one additional so called "30 amp" Chinese dimmer remaining
after the prior one smoked. This one had a circuit breaker and it did
go today, but not before it started smoking. As I said, I have a good
Astron power supply on the way to replace, but I still had the dimmer in
place until then and outdoors.

This time, I decided to open it up and see what's going on. As others
have said, the Chinese tend to exaggerate ratings so "30 amp" was
probably far from it, but I was surprised what I saw internally:

two HY1707 Mosfets
an LM358
a 78L05
a 555 timer

At 12V, 7 amp load, it seems like it should have been able to handle the
load, but I am wondering that since I was driving it with a switching
supply, maybe that somehow affected the dimmer? By the way, the burnout
was one of the HY1707's. Perhaps they actually need a heatsink instead
of just being attached to the circuit board?

That's absolutely all for the Chinese stuff. I had a constant voltage/
current module on the way, but not even going to open it. Can't trust
it anymore.

A device like that needs a proper heatsink. Even if the metal tab is soldered to the PC it's still inadequate for high power applications.