About the 12V LED dimmer, there always a lot of questions: which LED dimmer suitable for my 12V LED lamp? What LED driver should I use?
So now the answer is:
Firstly your LED lamp must be dimmable.
Second you must use a 12VDC LED driver, not a 12V AC LED driver if you want to dim.
There are only 12 DC LED dimmer on the market, no 12V AC LED dimmer.
If your LED lamp which input voltage is 12V AC/DC and it is dimmable, then you must buy a 12V DC LED driver and a 12V LED dimmer.