Hope this will help a little.
I just received my PI yesterday. I do not have a power supply yet.
On the other hand I have a multi pronged USB adaptor. I use it to charge my cell phone from the laptop.
This same combination runs the PI perfectly.
Also since you need a US power supply, "only difference" is AC plug differences and possibly 50 verses CPS power mains. Most now days will work with either 50 or 60 CPS.
All the above should be available at Radio Shack in the US.