I'm trying to figure out how to power a few devices during power outages. I've looked into UPS devices and also portable phone power banks. My biggest problem is how to compare the devices, apples-to-apples. The UPS we're looking at claims to provide 600VA/330w, and it has only 120V (AC) outlets. The power bank claims it provides 20,000 mAh. It has both USB ports and a 120V (AC) output. How do I evaluate how long each device will last? It would be helpful to know how to convert VA or W from the UPS and mAh from the power bank in like terms.
We have two devices to power. First, we'd like to be able to charge a Moto e4plus phone. The battery itself is rated to 5,000 mAh. It charges through USB, and as far as I can tell it draws 1.9A while it charges at 5v. A full charge takes 2-3 hours.
The second device is our cable modem. The modem is a Technicolor TC8305C. The modem plugs in to the AC mains and the label says it draws 1.2A. The modem itself does have the capability to use its own battery for reserve power. We don't have one, but I've attached a picture of one. Perhaps that might give a clearer picture of what DC power it actually consumes.