Electric Bikes - Renerative Hub Brakes

My mom has a chinease electric "assist" bike. It's an incredibly heavy yellow contraption with pedals.
However, the cool part about is that both brakes provide a boost to the battery when you brake. I've been looking at various dynamo hubs and I don't see any of them integrating braking, are there some no-name brands I should be looking at?

Shimano Nexus, Schmidt don't have any brake attachments. I found a Sturmey archer hub with a hub brake, but it doesn't seem to provide a boost to the dynamo.

Are hubs like this really only available for custom oem bikes? Or is this some sort of a marketing feature fooling me?

I have a guess about how your mom's electric assist bike works. It doesn't include what people usually call a dynamo hub, because these are made for running lights at about 3 watts of power. With one of these, you wouldn't get enough power to charge your motor's batteries to any useful degree... if you're lucky you might get an extra 100 yards or 100m of range.

However, electric motors and electric generators are essentially the same thing, although they require different controlling electronics. You can build a bike with a controller that serves both charging (dynamo) and discharging (motor) functions. with an electric motor large enough to give a useful amount of power assist while riding, you will also have something that can contribute substantial stopping power and in normal use it may recover up to 10% (possibly more) of the battery power (and pedal power) you use to power the bike.