I always put my charging block in my checked bag on shortish flights, and I don't know of any rules prohibiting this anywhere in the world. In which airports have you experienced pushback? Did you request citations from official policies/regulations? I include my backup computers, phones, and all of their peripherals in my checked bag. I don't own any power banks at present, and I understand that they must be carried onboard pretty much everywhere (i.e. just like spare batteries).

I have a transpac flight (so longer than my battery will last without help) today, so I'm wondering if I can stow away the charging block. This particular flight is on Japan Airlines, but I'm assuming the USB-C port technology is on par with what United currently provides.

While I might seem obsessive about this, I always fry to keep my personal item as nimble and simple as possible. It's not that an extra 8 oz kills me; it's simply a desire for minimalism on this front (i.e. if I only have a computer, a phone, a USB-C cable, a small/consolidated bottle of medicine, my passport, and a change of clothes, it's super easy for me to access anything at anytime, without shuffling).