I had the same thing happen shannan. What I worked out was that the pass through needs close to 2 A to run and the charger puts out either .5 or 1 A. You risk doing some seriouse damage running it off of your computer. I am using a power usb that puts out over 2 A or you will need to get a usb wall wart that puts out over 2A.
For personal reasons.
Just an FYI: I'm not sure if they are all the same, but the iPad wall warts meet this spec and I have only ever seen one car cigarette lighter USB nub that would put that much out... I can't remember what it was now, but I found them on Amazon. Unfortunately, you will have to sift through the reviews to find that valuable information, that's what I can't point you directly to it at the moment. And like you, I'd worry about using the computer USB port for that as well.
Here is a link to one that will do the job: $12.30 Universal 2.1A AC Power Adapter 4-Port USB Travel Charger (UK/Euro/US/AU Plug) - white / wall charger at FastTech - Worldwide Free Shipping
I ordered one of these: