Hi all. I am new to this forum but thought I would post something helpful. I am a type 1 diabetic and I use the dexcom seven CGM. Recently I noticed that my receiver unit stopped charging. I called dexcom support and they said they would send me new charging cord, which would take a week to get to me.
Unsatisfied with this, I went to every electronics store in Colorado trying to find a compatible charger. (FYI there aren't any, dexcom uses a very proprietary plug) so I was out of luck and assumed I would have to back to my old "test 10 times a day" routine. Then it occurred to me that the USB cable supplied with my dexcom might somehow be converted to charge my receiver.
(it doesn't by default, and I have no idea why). So, I pried opened the end of USB cable with a putty knife and saw four wires. (red, black, green and white) I knew that the red wire is supposed to be the 5 volt power supply in a USB cable, but I compare where that wire was positioned to the now useless power cable dexcom was replacing.
Turns out the red wire in the USB cable wasn't being used for power in the USB cable (no idea why) so I just snipped it, hooked it on to the same pin position as I observed in the actual power cable and viola, it started charging my receiver! So I closed the plug/tip enclosure and had a functional USB charging codd.
I have no doubt this is not approved by dexcom and don't pretend to be an electrical engineer, it just worked nicely for me.