dynos are generally considered to be a current source. Obviously, the amount of current and voltage they put out varies somewhat with speed. But the voltage follows the current and the hubs can only put out about 500mA. Which is why I wouldn't expect to see regulation in a dyno light. It just wastes energy.

The German lights don't seem to have a blocking cap. The ones I'm familiar with do have some kind of boost circuit. It isn't really possible to generalize about dyno headlights since they appear to all be different.

I don't doubt the person above that reported success. You can overdrive a modern power emitter. It just reduces the efficiency and lifetime. Best to limit the power to within the recommended current limits.