I purchased this one.

https://www.amazon.com/gp/product/B073XYYYWR

There's another model that has two USB inputs, so you could use two power banks or use one and draw more amps.

I was skeptical, and the packaging made me even more so, cardboard & crinkly shrinkly, but I plugged it into my cheapest 5200mah power bank and measured the voltage. 8.8 volts, which is just about right (I've gone as high as 9.2, but prefer not to). Notably, the needle on my trusty voltmeter did not wiggle. Also noteworthy, it didn't seem to need the recommended 3 amp draw. It comes with a 3 amp wall wart if you just want to plug the camera into the mains for power.

It comes with a bog standard dummy battery. The step up converter is tiny, not much thicker than the cable. Plugged in the camera (Panasonic G7) and waited. The 5200mah power bank ran the camera for 156 minutes, or two and one half hours. Not bad--you are going to lose some power in the conversion so don't skimp on the power bank. I'll do some tests later with my RAV 20,000mah bank.

Camera ran cooler than expected.

So there you have it, easy, lightweight power from USB. I had been using 9 volt packs with stacks of Panasonic 18650 cells (runs forever....). But this is really easy.

You can buy adapters for most cameras, and considering the fact that it comes with a dummy battery, the price is cheap. Will it burn out? Interesting question.

[Added formatting and photo, VK]