At one time Radio Shack use to sell a portable power supply which would allow you to switch to either 9 or 12v. They no longer carry it.

I am looking for such an item seeing that most shows hate to see power cords running along the floor (which I don't blame them) and their tables are not located next to a wall outlet.
So, I need ideas as to where to get such a device for there still has to be something similiar floating around.
My google search was more confusing than helpful.
A friend told me about UPS, but they too need to be plugged into a wall socket, which is what I am looking to get away from.
Thanks