Printing and designing in 3d allows a designer to build a case and mechanical parts around whatever is available. For example, I used an ultracapacitor from a Coleman Ultracap Screwdriver. It was simple to design and print a hollow cylinder to accept the capacitor--this would have been a major challenge a year ago.
I used Autodesk 123d (free) to design the 3d parts. Files are available here:
If you want to see how I regulate the incoming voltage, look at this instructable: