Ron, I think you can connect your PC to the 4208, the same way I connect my 3210.
It's a 18 or 19 pin (I forget what it is) plug
on one end, (whether it's a male or female depends on the NMEA 0183 plug
on the back of your plotter.), and the other end goes to the PC.
In my situation my Power/Data (NMEA 0183) cable in all in one, so I have to use a powered adapter cable to make the connection. In your case they separated the cable, with one cable for power and one cable for data...you will probably use a non powered adapter.
On the PC end of my cable it has a serial
connection, because I have a dedicated serial port on my PC (I ordered my PC just for this situation). Unless you have a serial port on your PC, you may have to use a USB to serial adapter on your PC. You might be able to to use just USB, but I think not.
I did a search for the Garmin adapter I was looking for online, and found several sites that I could order it from. Garmin does not sell these adapters from their site, so you have to order them from 3rd party sites.