I have a home made amblilight setup powered by an Arduino Uno, it has a string of 50 addressable LED's, is this the kind of thing you have?
My Uno is powered by a nomral 5V USB power supply, I just made sure to buy a good quality one from a UK supplier and its fine, the Uno draw almost no power at all. I am a bit of an electronics hobbyist and have watched too many Youtube videos about Chinese power supplies to ever buy one again, lol.
The LED lights themselves in my case are separately powered and for them I bought a laptop power supply rated to in excess of the required power, I think from memory my lights are WS2811 and require 12V and the load is over 5A so I had to buy a pretty chunky laptop PSU - from memory I bought an OEM (can't remember whether it was HP, IBM etc) these are a decent choice as they are rated for continuous load. Personally I would avoid the generic ebay ones as although they are much cheaper they are very variable qulaity wise.
In other news, if you have an HTPC and haven't already got an Ambilight setup you should definitely consider it, very cool, wife loves it.
Cool beans
Chunks