The wagan twin usb is cheapest at amazon.com
The following amazon link is a 35 percent discount off any wagan twin usb accessory or charger. The coupon loads automatically.
Wagan Twin USB/DC Socket Traveler's Adapter transforms one cigarette lighter outlet into 2 USB and 2 DC outlets. This travel adapter includes a built-in LED indicator. The adapter head can swing up to 180 degrees.
