Double check that you have a proper working, good quality desktop power supply. https://en.wikipedia.org/wiki/Power_supp...

Set it to +5V DC and double and triple check the power and the polarity with a multimeter.

Connect ground of the USB port with ground of the external desktop power supply.

Maybe you can use just a usb cable but I preferred to use a cable with a device. I used an FTDI breakout board from sparkfun because there the pins are relatively good accessible.

Supply the USB device (I suppose on the port that caused the problem) with 5V from the desktop power supply on the 5V pin of the USB plug.

The LEDs on the FTDI light up and it is recognized by the Mac.

For whatever reason the second USB port got reactivated, too. It works without the need to provide the connected USB device with external power.