The spec is 12v 1000mA : Outside -, Center pin +.
If the power supply is more than 1000mA (1A) then that's also alright (I have one that is 1.5A and I split the output to charge 2 readers at once).
The original is (you can find these on eBay as well):
Thompson Consumer Electronics
Model No: 481210003CT
Input: 120VAC 60Hz
NOTE: There's a LEI brand with the same model number that has an incompatible plug on it.
If you're able to do some soldering then, as a last resort:
1. Get a 12v switch mode power supply from eBay (assuming you are willing to wait 1 month for delivery) for about $3
2. Purchase a new plug that fits the reader (0.7 x 2.35 mm) - see DigiKey part # CP-012-ND
I've built up a few like this for myself over the years without any problems.
The advantages are that it's smaller, lighter, more efficient and accepts 90-250v 50/60 Hz input and you can choose the type of plug - e.g. you would most likely want the EU version.
Hope this helps.
Last edited by mark844; 12-16-2011 at 04:25 PM.
Reason: added advantages