(I mistakenly believed that USB-charging was possible with the 70b, but I see now that the AC Adapter is required for charging. That is a mild disappointment.)
I'm sure you'll be pleased to discover that the 70b does use USB-charging. Using the supplied USB charger is faster than using a PC's USB port.
Much faster @ 1.5v
Well, I've made an interesting discovery - when using my Amazon basics USB power adapter, the Archos thinks it's just being charged up on a plain old USB port (and had the courtesy to tell me it was on a slow charge cycle). This doesn't entirely surprise me. I think I read something once about pin assignments on certain chargers which are cut so that the charged hardware knows it is not in a data port.
What surprises me is that charging up WITH the official adapter, from <5% charged, results in only about a 10% charge per HOUR. The Archos doesn't tell me it's on a slow charge cycle, but it sure seems that way.