Not exactly what you want, and limited to UK use, but I carry one of these around with me most of the time: https://www.themu.co.uk/ https://www.themu.co.uk/ I

Not exactly what you want, and limited to UK use, but I carry one of these around with me most of the time: https://www.themu.co.uk/ https://www.themu.co.uk/ It's even smaller than I thought it would be, and so much more portable than a normal UK plug.