That would convert an internal header into two external ones.
Edit.
http://www.box.co.uk/NZXT_Internal_...1018433.html?gclid=CMPDxq2n99ACFe-37QodmMkGTw
There you go, an internal USB hub. I can vouch for it too, I used to have one.
Fan speed reducers can go straight from either the Fan header on the motherboard, the H80i or from Molex or SATA power - not USB. Or do you mean a fan controller like one that goes in a spare bay?
I've not heard of one running of USB. If you have an H80i the fans are connected to the pump housing and controlled by corsair link. The H80i then connects via USB to the motherboard (for control) and to the CPU fan.
I run an internal USB2 to external off my motherboard as my G29 won't work on USB 3 so yes they're available as above but I'm not sure if that's exactly what you need.
Alright, let me explain what I'm trying to do with what I have. There might be another way of doing it. I've build a budget AMD rig for my bedroom. I like my setups to have case fans with lights so it's red themed with two fans in the front, and one at the back. I connected the two rear fans but at 12V which meant they made to much noise, so I purchased a NZXT GRID unit to quieten them. This connects via a micro USB into the device to a motherboard USB header. It looks it can be powered another way, but I don't have the appropriate cable (if it did come with one it's gone missing).
This setup was fine until I decided to buy a more efficient CPU cooler (the AMD one is atrocious for noise). Along came the Corsair h80i. This needs a motherboard header but the board only has one. Taking out the GRID as it now can't connect has made the two back case fans loud again which comes to the thread I posted.
What is the preferred solution. Find another way of powering the GRID, or buying that adapter and connecting both devices to it?
This is the updated header to what AlienALX showed you I own the old one already but this new one is much better https://www.nzxt.com/products/internal-usb-hub
Yeah I'll confess I bought mine absolutely ages ago. That one looks much nicer. Twice the price, though.