You may be able to find a similar adapter. The PSP adapter outputs 5 V DC at 2 A. I believe the polarity is tip positive, but I'm not 100% sure on that. There's a symbol next to the power connector that indicates the polarity. Refer to http://support.radioshack.com/support_tutorials/batteries/pwrgde-2G.htm to ensure you use the correct polarity.
Also, you may want to consider getting a USB cable that has the power connector built in, since they work really well as a portable charger.