Ken,

How about just wiring up a plug to your present13.8 Volt
DC power supply, assuming you have one. Alternatively, you could fix
the wall wart, which may be one that puts out AC. If so, you could
rectify it with some diodes, filter it with about a 1000 microfarad at
16 volt electrolytic capacitor, and use a LM7812 3 pin regulator, which
would hold the output voltage to 12VDC. A LM7812 in a TO-220 case is
good for over 1 amp current draw, and so would be fine for your Icom.

This has the benefit of being cheap, easy, and being a learning
experience. Give me a shout if you need a schematic or a physical
diagram of what I am talking about. The whole thing would take 15
minutes and maybe five bucks for parts, tax included.