Dude...

Leading edge or trailing edge is the difference of which part of the wave form the dimmer cancels out to reduce the average current in the circuit, thats exactly what i was describing in my comment.

>they switch said AC current on/off at an adjustable time after the start of each half cycle, thus modulating the width of the pulses of current sent through the circuit

Leading edge vs trailing edge is just whether the circuit is turned back OFF during the half cycle, or turned back ON during the half cycle. You literally dont understand the technology enough to recognize a description of how it works. If all the ones youve installed have been leading edge or trailing edge, theyve all been solid state dimmers.

Also, he needs a 120V AC to 12V DC adaptor either way, so honestly he could use an AC dimmer OR a DC dimmer.