Sure, you can pick up a new power supply at Radio Shack or the like. You can also get one from SlingMedia if you want to go that way.
You have the Slingbox PRO, correct ? The power supplies are not universal across all models, just want to be clear on that.
For the Pro, here are the specs from the User Guide (pg. 11):
You can grab a PDF copy of your manual here if you don't have one:
Here's a link to the SlingMedia shop page that has your power supply:
Take your Slingbox with you if you decide to go shopping for a new power supply in person. You'll need to match up the barrel plug size so you get the right one.