I believe the PS/2 to USB adapter you're using only works with a Logitech mouse. When you plug a Logitech mouse into it, the mouse detects the adapter and sends the signals differently so that it works. It can't be used with a keyboard or in this case, a joystick.
There are generic PS/2 to USB adapters on the market but they're usually very laggy and not recommended for something like a joystick.
You're probably going to need to find a modern PC or at least a motherboard that has a PS/2 port. They're still on the market, just much less common then they used to be.
EDIT: I found some documentation: http://arcadecontrols.com/arcade_powerramp.shtml
Supposedly, it has a PS/2 passthrough. You can plug your PS/2 keyboard into it and then plug it into the computer.
GroovyMAME support forum on BYOAC
Edited by krick (04/06/18 08:50 AM)