USB has been around for a long time, it seems. Longer than I'd originally thought. For fun I wanted to try and get this relic of a PowerPC into the less-than-stone ages and, well, plug things in without having to reboot. USB would provide this and I had a few devices to try out.
There's information on what OS' support USB here at lowendmac. My mileage varied... but I actually think it was because of faulty/old hardware rather than software incompatibilities.
The card shows up in System Profiler but there is no power on the USB bus. I plugged a $10 HP Mouse in and the LED/Laser didn't glow. It seems this card is only good for Beige G3s or higher? Or could this card just be faulty?
OS 9.2.2 had installed and loaded the USB extensions... so it seemed that it wanted to do something with the card, but failed.
Adaptec Duo Connect PCI Card AUA-3020
This card comes with 2 FireWire and 3 USB 2.0 Ports. I plugged it into the PCI slot and booted up. I had already installed OS 9.2.2 with the previous USB card in, so the USB extensions were all there. Plugging in the same HP Mouse saw the light glow underneath. It worked!
Right-click just acts as normal click, so it effectively becomes a one-button mouse. I'm sure you could install something like USB Overdrive to make the buttons and scroll wheels more functional.
Opti FireLink BG-3800-00 UH-275
It worked perfectly on installation. No configuration necessary. The mouse lit up and was functional straight away.
OS9.2.2 and USB Keyboards/Mice
The USB cards will apply power to the bus very early in the boot process, but the devices wont actually work until the last icon on the desktop is loaded. It's still recommended to use your ADB equipment (or at least keep it for emergency purposes.)
Both the HP USB Mouse and Apple Keyboard (from a future iMac) worked perfectly fine.
LITE-ON DVD Drive
I plugged in my portable eSAU108 DVD/CD Writer. On the Adaptec Duo, I only got a flashing red light on the unit. It seems that the card does not output enough power for the device to function correctly. On the UH-275 USB Card, the drive worked perfectly.
Further research indicates that the drive has a smart USB power detection feature. The LED will flash red if it needs to suck power from two ports. So it seems the Adaptec correctly limits the power, whereas the UH-275 can push out more milliamps.
Downloadable from here, I assumed this would give me left-click and scroll-wheel mapping... instead it just stopped the HP Mouse from working at all. I gave up on it pretty quickly.
Does the USB get passed through to the DOS Card?
No. Even worse... if you have a 2-button mouse on the USB, the second button does absolutely nothing on the Windows side. It makes perfect sense but can be really confusing when you still have to command-click to get a context menu.