Question mixing USB 2.0 and USB 3.0


Jun 12, 2015
I have an old PC with a motherboard that does not have a 19-pin motherboard connector for USB 3.0. I added a card that has a single port on the back to supply USB 3.0 to the case. I bought a specialty cable with two type-A cables on one end and a 19-pin motherboard connector on the other. I have a device, which fits into a standard 3.5" panel (originally devised for floppy drives, I think) which has two USB 3.0 ports fed by a 19-pin motherboard connector. However, if I've explained all this correctly, you'll see that the 3.5" panel device can only offer one active USB 3.0 port at a time.

I could buy an adapter (StarTech makes one) that connects one USB 2.0 motherboard connector to a type-A cable, which I could use to attach to the unused end of the specialty cable, so the 3.5" panel device would offer USB 3.0 on one port and USB 2.0 on the other. Keep in mind that the USB 3.0 would be fed by an add-on card and the USB 2.0 would be fed by the motherboard, two very different sources.

So my question is: would this present an electrical issue, given that the 19-pin connector would be fed half by USB 3.0 and half by USB 2.0? Or should I be satisfied with having one USB 3.0 port?

Here's my cheesy diagram:

motherboard USB 2.0 -> USB 3.0 type-A
---------------------------------------------------(specialty cable) 19-pin motherboard connector -> 3.5" panel with two USB 3.0 ports
add-on USB 3.0 card -> USB 3.0 type-A

P.S. The reasons I did not buy an add-on card with a 19-pin motherboard connector are 1) I already own the card and 2) it uses a TI chip and is very reliable unlike some other cards I've tried.
there shouldn't be an issue with power where it could damage anything.
but there may be issue with not being able to provide adequate power to some 3.0 devices.
also if used for USB drives their performance could be severely limited.

the best option besides purchasing a decent motherboard would probably be to just get a PCIe USB 3.2 card with enough ports for your 3.0+ devices.