Product should come with a USB power cable / adapter PER CAMERA
I recently purchased the 4-camera product kit. Inside that package was ONE USB power cord / adapter. It goes without saying that a product at this price point should include wired powered options for EACH of the cameras in the kit. Particularly, since the AC Adapter is an odd 9v version that is not readily available at your local Walmart, Best Buy, etc.
A power cord / adapter is included when sold with individual cameras, but not bundled options. Of course, it's not price condusive to buying the cameras separately. You'll end up spending much more on the whole package.
Re: Product should come with a USB power cable / adapter PER CAMERA
WHile one can ague the merits of more than one charger, it's not unique. The chargers use Qualcomm QuickCharge technology which means both 5v @ ~2A as well as 9v @ ~1.5A. That's the same charger type as with many current/recent cell phones such as those from Samsung. They can be purchased fairly inexpensively from a wide variety of places.
The fly in the ointment is the need to use a quality charger so as to not damage the camera. In any event, use of a non-Arlo accessory can void the warranty. Just be careful and prudent and you shouldn't have any issues.