changing 12v halogen lighting to 12v LED
When I did this I used 4x 3W rated LEDs in series using only about 8W on an Alumclad thin strip for illuminating under each wood step and used a 30A Sh diode bridge and high ripple current rate cap >16V with no series resistors and the power was just right and not using all the LED rated power with no flicker. I think I had a 200W Schlumberger transformer. But this takes some skill with Ohm’s Law and pre-made 1*4” alum PCB with Cree LEDs. If you have similar 4S power LEDs on a board, you can try a test with a Bridge and 1mF low ESR cap and maybe a 1 or 2 ohm series R after the bridge. 

You can also get outdoor coated power StripLeds which are less efficient since the 4th 3V drop is replaced by resistors  for much wider voltage tolerance to 14.2V and power from a Bridge and 1mF low ESR cap per transformer  


or consider these and save all the underground expense.


If you define the lighting , LEDs or luminaire, and power per drop,  better solutions may exist.