How to build my own 8V 6A PSU using laptop charger
It would be harder than starting from scratch.  Dropping 19V to 8V is fairly easy.  Increasing 4A to 6A is harder.  You would need DC to DC conversion circuit.  This is not easy and less so at that power level.

LEDs don't need real great power regulation.  You can run a transformer with enough current capacity to drive the LEDs and a full wave rectifier.  You can probably get by with very little if any filter caps.