Trans Am Bike Race / TransAm / TABR

One other factor- mains power in the US is shit, 120v. It takes significantly longer to charge stuff.

I thought that was an interesting point. I typically stay in a hotel for 5 hours, which is how long it takes to charge a 10Ah power bank. If it takes twice as long, then it would make a dynamo much more sensible.

I googled it and it seems that it depends on the charger with bigger kit (laptops) more likely to take longer while phones should take the same amount of time. But I'd need to be more certain if I was doing it.

I've no particular desire to be an advocate of not using dynamos but there tends to be lots of confirmation bias around, people who have spent money and time on dynamos want to believe they are the best option (and also for people like me who have explored alternatives). As a result I think a lot of new riders getting into this kind of thing think they need a dynamo when its probably not the best option for them, especially if their long term power output is not very high.
However, i suppose that in the grand scheme of things, it's not the most important decision.