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.