For a time, macbooks had opto-isolated USB ports[0]. I think they don’t anymore though.

[0] https://github.com/usbkill/community/wiki/Consumer-Laptop-Ha...

Call me highly skeptical. Every reference I've seen to this claim seems to point back to usbkill.com making it itself.

The problem is: optoisolators are very slow. Building one which goes faster than 12Mbps would be nontrivial; I do not think such a thing existed in 2014 (which usbkill is claiming). This implies that Apple has alien technology.

I think it's something else.

  The problem is: optoisolators are very slow.

Many are but they don't have to be - an optoisolator is just a zero-length fiber optic cable. Ain't much higher bandwidth than a fiber optic cable.

Not saying apple laptops ever had optoisolated USB though.

IMHO the problem with isolating USB is the 480Mbit ("USB 2.0") bidirectional signal.

12Mbps/1.5Mbps is easy. ADI has an integrated magnetic isolator chip. For hobbyist use you can get this assembled on a board ready to use as an ebay special.

The 5Gbit of USB3 is two unidirectional links and so is also easy (monoprice and elsewhere sell optical USB3 cables).

And lest you think you'll isolate at 5Gbit and then use a hub to translate to 480, USB3 doesn't work that way - the backwards compatibility is provided by a complete USB 2 bus in parallel.

For general isolating (say an electronics workbench), it's easiest to consider the USB host floating (eg a dedicated bench computer), and rely on ethernet (T or SX) for the isolation.

Beyond that the host has to supply 5V to the USB device, couldn't you just cause some damage by sending 200V on these lines? You might only fry the USB power supply but that's enough to be a major pain.