I have a SuperPid/G540 setup running Mach3 on an old Dell Optiplex GX620. Everything worked great except spindle on/off... I was having to do that manually. I assumed the issue was wiring or Mach3 configuration, since that was the only issue... bad assumption. Eventually I got around to testing the parallel port output pin voltage and it was 3.3Volts, not 5 like I read everywhere that I needed. Researching around, I couldn't find a readily available (e.g. Amazon prime) parallel port card that was known to work. So I rolled the dice on this $9 Shinestar branded card:
https://www.amazon.com/gp/product/B079939BLV
and it's working fine. I did install the parallel driver that came with it, disable the motherboard parallel port, set the driver for the new card to use LPT1 (LPT3 was the default), and update the card address in Mach3 ports/pins, but I gather that may be needed for any add in parallel port.
It is a PCI (long motherboard connector) and not a PCIe (short motherboard connector) card. In my research, it seemed to me that my odds were greater at getting a 5 volt card if it was PCI rather than PCIe. Not sure if that's really true or not.
Anyway, just FYI, and sharing info I wish I'd have come across when I was trying to sort this out.