This is a 12V / 1.5 Amp linear power supply with an in-line filtering unit. Good upgrade for those with Beresford DACs or other DACs that work with 12VDC. It has a 2.1mm DC plug, which is user-replaceable. I think I also have a 2.5mm plug, will confirm.
£110 new, yours for £42.50 incl. P&P.
Will also fit into older Airport Express or Extremes.