Setup my Dynamo light and USB charging today.
Used some telephone cable from jaycar @ $0.60 a metre it has 4 insulated wires inside it, paired colours together, soldered then crimped into SP hub plug:

Those wires split out at top into 4 mini banana plug sockets, soldered and heatshrinked.

USB converter and light have banana plugs on the end and I’ll leave them both plugged in all the time while riding (can unplug for transit/move between bikes if I wanted to)
Wider view:

Took it for a ride around the block, takes 20 seconds for USB charging to start, but charges exposure diablo till about 7kmph, powered GPS fine till about the same (not at same time, but it might work at high speeds)
Once below 7kmph GPS beeps saying “external power lost” and you gotta push a button to revert to battery and stop it turning off in 30 seconds, it seems if you speed up quick enough it goes back to external power but on a steep climb or single track I’ll just let use batteries.
Both still worked with light on but I’ll have to wait till dark to see how much light output is affected.
I’m pretty happy, going to see how long it takes to charge the diablo on some rides soon.