Power supply for UNO R3 controller

I recently purchased the UNO R3 controller. It arrived ok but no means of powering the board. Must I order the 9V DC Power supply separately? When I look on Amazon this is described as a replacement cable for the UNO, which gives me the impression that the cable should have been included. After all when I buy a kettle I don't need to specify that the power cable be included.

Can the UNO be powered from my computer via a usb?

My Arduinos (and many other similar systems) draw power from the USB port. You should check out this page http://arduino.cc/en/Guide/HomePage and follow the link for your OS.

Whether you get the 9V cable or not probably depends on whether you ordered a kit or just the plain board. My first Arduino was in a kit that had a bunch of accessories included like a breadboard and base that holds both R3 and breadboard. It also included jumpers, resistors, LEDs and a cable for a 9V battery.

Enjoy!