Slightly off the topic of Robotics, I have built a power supply to take USB or a 14v power pack and make a usable end out of it for running motors, fans, and other useful equipment that needs to be tested before installed into something.
As seen on the Google page:
I wanted to make a power supply to be able to plug into multiple sources for DC voltage. Two voltages are made from the device, 5v 200mA from the USB, and 14v 200mA from the power pack. I do not have a power regulator making the 14v into 5v, but that would be a nice touch in the future.