Another handy gadget is a Charge Hub. You plug it into the wall and on the round hockey puck looking thing (I'm so articulate), there are about 5-7 USB ports (depending on what one you buy). When we go on vacation it has been a lifesaver, with so many devices to charge now and not all hotels have added USB ports to the outlets in the rooms. There are all sorts of versions besides Charge Hub, lots on Amazon.
i would bring the plug. We have stayed in several rooms that had USB ports, but they didn't work.
I also bring a rechargeable battery to take to the park with us so we can recharge the phones during the day if needed.
Similar experience here, I always bring a plug, because the ports may not work. But as Slippery Pete would say...you can always get electricity out of the holes: