Buck regulators and led
There are literally thousands of different LED driver solutions today. Most are either DC-DC boost, buck or line isolated AC-DC, constant current, (fixed, or dimmable).  power Factor Corrected (PFC) on AC (or not)

The latest trend is direct offline AC-DC without isolation for protected lamp solutions only.

These come with all the above extra features for low incremental cost.
The value of using more expensive portable AC PSU's to be modified for LED's or custom external drivers must compete with the great advantage of offline flyback dimmable, PFC solutions or require the transformer isolation for human handling with >=3kV isolation.