I just bought a few of these:
http://www.allelectronics.com/cgi-bin/item/PS-913/480/9_VDC,_1.3_AMP_POWER_SUPPLY_.html
Very nice and inexpensive. You will need a 2.5mm power jack on your
P3, or change the plug on the power supply. I bought some extra for
my other 9Vdc devices.
Ivan