Just purchased 2 Express 4K+ units. Keep getting LO POWER every so often plugged into USB port on TV. I have to unplug the USB and re-plug and that fixes the issue. Now you say well just plug it into the wall outlet. Well, the outlets are 12" off the floor and the TV is 65". The cords supplied are both too short to accommodate this. Really ROKU? This is the real world and these cords just don't cut it. Yea I know, Amazon, buy why?
The easiest thing to do would be to use an AC extension cord and plug the USB power adapter into that.
If the AC adapters are USB, you can use any USB extension cord, which may be less unsightly than an AC extension cord.
In fact, if the Roku itself uses a USB port for power and not one of the barrel connectors, you can just use a standard USB cord as long as you want.