how can I convert my AC under kitchen cabinet lights to LED lights?
These are currently available:- "Gx53 LED Light Bulb 110 Volts 5 Watts Warm White with Lamp Base for Ceiling Downlight Under Counter Lighting (5 Watts)" and will hardwire directly into your existing 120V wiring.
It also removes the requirement for AC/DC transformers which are just another link for failure.