Wiring DB25 1205 breakout

The manual stated:
"The power supply input port, it can set up the single or double power supply. J4 is the isolating source (GND) and Isolating source(+)
Jn1 and JN2 are connected in the case of a single power supply. The +5V and the isolating source (+) will be connected.
The GND and the isolating source (GND) will be connected.
If JN1 and JN2 is not connected (open)
The +5V and the isolating source (+) will NOT be connected. The GND and the isolating source (GND) will NOT be connected"

I find this rather puzzling: As far as I can see there is only one connection for 5 Volt supply. Again as far as I know the DB25 connector has room external power supply on pins 9 and 10. But these pins are usually not connected.
So; what does all that bla-bla in the manual mean?

Other than in software these hardware thing can blow up in your face, that's why I'm asking.

J1 and J2 are for separating the the the power sources for the parallel port side of the card and the machine side. If you don't care about isolation and only want to use one 5v power supply you can leave those jumpers on.

If you take those jumpers off you have to connect a 5v supply and ground to the 5v+ and VDD terminals and their respective grounds.

J4 is a little fuzzier on its definition, but I suspect it is for setting the inputs for sourcing or sinking inputs (basically taking a pull up or pull down resistor in or out of the circuit.