warpigs -
I just went through a power supply shuffle. I lost the power supply to a Fatar midi keyboard. All it says by the hole on the unit it "DC IN 9V". Gee thanks guys, no mA, no polarity, and Fatar didn't return 2 emails I sent them.
Here's what I found after talking with my dad who is an Electrical Engineer:
You can use any power supply so log as it matches the numbers. So in your case, try to get a hold of a 21.5V 500mA power supply. You can use one that has more mA (eg. 21.5V 750mA), but if it shows less mA, you probably will overheat the power supply and it will stop working because it can't produce enough current. Also, you need to make sure the tip that plugs into your device matches the +/-. So, the tip may be - at the center and + at the outer or vica versa. So you have to make sure that matches. ALSO (who'da thought there'd be so much involved in getting a power supply :0 ) you need to make sure the hole in the tip is the right size. I've seen them 2 different sizes.
Using that info, if you just can't find a match of all those parameters, get the voltage and mA rating as close as possible. If the tip doesn't match the +/-, you can cut the cord, strip the 2 wires, and cross connect them (this will switch the tip from + to - or vica versa). If the hole isn' the right size, buy a cheap power supply for the right tip and cut it off and connect it to the one with the right voltage and amps.