I'm guessing if I accidentally got a pci-e one, it wouldn't work in any of the USB ports I would connect it to (as, to my knowledge, I only have USB ports), or

I'm guessing if I accidentally got a pci-e one, it wouldn't work in any of the USB ports I would connect it to (as, to my knowledge, I only have USB ports), or do they generally fall back to working as a USB device?