The BEST of the best . . . . like 47Labs in approach but so much better. You pay for circuit design, parts choice and violin varnish treatment. It's powered by a 12V battery (not included) which, even with the battery charger, will cost you a lot less than ‘audiophile’ power cords and a power conditioner.
The only amp I've heard which beats the BYOB Altmann amp is a high-end WAVAC. Not certain I've heard a DAC beat it.
I own two BYOB amp and DAC combos, this one was in my second home (now gone), so no need for two, very low hours. Selling each for $1,000. The BYOB amp is capable of 10W/8 ohms, up to 20W/4 ohms.
These can only be bought from the manufacturer, Charles Altmann, at the current price of $$$$$$$$$$$. It's rare to find on the second-hand market. Check out the reviews at Altmann's site, or elsewhere, they're telling the truth, it is killer.