So I'm looking at these USB addons that fit into a 3.5" floppy bay and bring USB 2.0 ports onto the PC case front panel, and I can't figure out why they put a molex connector on there. Each PC case essentially has / had front panel USB 2.0 ports built-in, and it only features a cable that you then plug onto the motherboard 9 -pin USB connector and you got USB 2.0 on the front. There is no extra power required. The front USB ports are usually soldered onto a small PCB along with one or two added capacitors (I'm guessing those are required due to the cable length), but that's it. USB 3 addons seem to be straight-through, but USB 2.0 ones seem to use the PCB with added capacitors and that molex connector, apparently for some kind of power. But why?
Example:
Example:

