Chris, the supply outputs 18.5VDC. Current draw is evidently max 2A thereabouts. The supply is rated for 4+A.
Pin connections, from memory, are symmetrical beginning, from outside to middle, with ground on the outside, followed by hot, with a signal line in the middle. The signal line is a trigger that terminates to a 6.5K or 6.8K resistor in the power supply.
I read somewhere that the Mini can be fed 12VDC and operate, so it looks to internally reduce the 18.5VDC immediately without use for any voltage >12V.
I suspect swapping the Apple supply for a linear unit would give a small bump in performance.