Hi, I am trying to make a variable power supply from a kit of sorts from eBay to see how it works out. I want to supply it with wall power, but my wall supplies 110VAC and the supply requires 15VAC. What is the best, ideally most cost efficient way of dealing with this? A transformer? They also sell things on eBay for very cheap claiming to step down 110VAC to 15VDC and I am curious as to why this is and whether or not you can modify it to output AC.