They are basic "dumb" USB outlets. Many newer devices are looking for "smart" outlets that do various fancy things to increase charge rates. Those devices will not work very well on the simple outlets. One of the things the smarts do is to regulate how much power is pulled. With a dumb outlet it is possible for a device to pull to much current (it shouldn't, but some do) and fry the outlet.
Most of the outlets I have seen have a LED on them that lets you know (maybe) if they are up and running. Assuming yours are like that, no LED means they either have fried or have lost connection to the 12V
empire. Loss of connection could be due to a loose wire / blown fuse / tripped breaker.
Bottom line is that the stock outlets should be fine for charging a phone overnight. If you need to power up a laptop computer and do video editing with it, you likely will need something a bit more sophisticated.