Forgive the newbie question, I'm pretty new to the whole bike scene. I've searched for an answer, but have not been able to find the right combination of search terms (and I just don't have the foundational knowledge required to determine what situations I'm finding are directly analogous to my situation).

What do I need to do/buy to charge a USB device off of a Shimano Dynamo Hub and a B&M Lumotec Topal Senso headlight?

My setup:
Shimano HD-3N30 dynamo hub
B&M Lumotec Topal Senso headlight
B&M Toplight Flat Plus rear light
The hub is connected to the Topal. The Topal has 2 auxiliary (i guess thats the proper term?) power leads. The Toplight Flat Plus rear light is connected to one of these auxiliary power leads. The other auxiliary lead on the Topal is available.

I would like to use the Topal's 2nd auxiliary power lead to charge a USB device. How can I do this?

I've searched for such an answer but have only found commercial devices that plug directly into your dynamo hub (or require you to splice in to the existing hub->headlight wires which I'd rather not do). I have been unable to find a USB charging device that explicitly calls out its ability to plug into a headlight auxiliary power output.

Thanks in advance!