I have built a small solar panel, 12V no load output, 1.4 A short circuit current out put. I also built a switching voltage regulator based on an LM317 adjustable regulator. I bought a USB connector at Radio Shack (voltage only), but when I try to charge my cell phone or my Kindle, neither one indicates that it is taking a charge. I have checked that the voltage at the USB pins is 5V, and checked that I have the correct pin polarity ( At least, it is the same as my wall wart chargers.) I have checked the output voltage of the regulator while connected to the devices, and the drop in voltage is .01 V. I have no trouble running a couple of small fans (.18 and .16 amps) and a small LED flasher at the same time (I adjust the voltage output up for these 12V items). Any ideas would be welcome.