Ditto previous. I carry a 75W rated PS with one USB port; sometimes it works, sometimes the power craps out even if I'm not using the USB.
Each plug seems to have a variable breaker and if too much power is in use from other ports, it may not work. Unplug, try again. If practical, you could carry a lower wattage PS but I want minimal equipment and weight. Try the other plug. It's a lot better than EMpower or no power! A bit of attention seems to keep things OK.