Hi, if I recall correctly USB 2 was problematic on the G3 PowerMacs. So try to find an used "Orange Micro USB 1.1 / firewire" card (perhaps eBay) and install it in your computer. Then connect your printer to the USB port. I'm assuming that you are using an older version of OS X, so the driver for your printer may not exist for your configuration.
Sorry, but this item cannot be used on the iPad Mini. The Mini DisplayPort on the adapter will not work with a Lightning/30-pin connector. Here are some links that may help you find what you're looking for: http://goo.gl/Lt0EXB http://goo.gl/05aWgM