Well, if they're anything like the USB to serial adapters, then they should work just fine. I even brought a 4 port serial to USB adapter to C4, which worked fine with TCPSer.
newegg.com and geeks.com both have those adapters, as well as knightdiscounts.com. Don't necessarily have to get one offa ebay.
On the other hand, Marko Mäkelä had quite a few issues with USB to serial adapters working with his C2N232 interface. Only a few USB devices seem to implement RS232 well enough to get it to work. I'm afraid USB parallel adapters might only implement partial parallel functionality as well.
they do not work with cbm4win. the problem is they do not present themselves as a parallel port, but a usb printing device.... they only work with printers.