My garage door has a 24VAC output off the main circuit board, so I purchased a 24VAC to 5VDC buck converter and soldered a USB connector on the output end to power my OG. They can be picked up cheap off eBay. I’ve been running it like this for over a year and never had any problems. It saves having to run a separate AC transformer to power the USB connection.
Here is a link to the one I purchased.
http://www.ebay.com.au/itm/Car-LED-Waterproof-DC-AC-DC-Buck-Converter-24V-12V-36V-8V-40V-to-5v-1A-5W-/281625925676?hash=item419236982c:g:i-sAAOSwopRYaPuu