Thanks. I did wonder if it was NTSC, but one such device was used on the composite input of a 90s CRT and that showed the colour fine. Which if it was NTSC I believe it would not?
All of the devices so far have been gaming related. Atari 2600 joystick with built in games, like this
https://www.amazon.co.uk/Atari-Retro.../dp/B076BS5WVN
and lots of similar and cheaper devices. "Retro FC Handheld" for example, which is a "NES on a chip" device with a load of games on flash memory. All cheapy tat, which might explain why it doesn't work so well. Just curious as to the technical reason and if they could be made to work better