Not sure why Alinco suggested 13.8 VDC and 30 Amps for a receiver, that is a bit odd. You need that kind of power for a 100 Watt transmitter, not a modern receiver.
Looking at the Alinco spec sheet here (DX-R8T/E Detail information
) they say the receiver only uses 1.0 Amp, much more in line with what one would expect.
Also note that the 13.8 is a “nominal” value, not really the only thing that can be used. For example if you use that radio in a car it might normally see anything from 12 to 14.4 VDC, depending on if the car motor is running and charging the battery or if the engine is off, the differing loads on the vehicle electrical system, etc. Again referring to the Alinco web page above it says “13.8 VDC +/- 15% (11.7 to 15.8 VDC)”.
Using the wall wart should be just fine. But make SURE the polarity of the jack is correct, there is no “standard”.
One thing to keep in mind is that many wall warts are poorly filtered switching supplies, so you might see some pretty hairy changes in your RFI. If you hear noise you never heard before look to the wall wart first. Since you have the Excalibur one way to check would be to lay the wall wart (unpowered) next to the Excal. Start the Excal and let a wideband waterfall history build for a minute. Power the wall wart (with it plugged into the Alinco) and look for changes on the wideband waterfall.