S video? Do you mean the PS/2 port?
They look a lot a like but they are not compatible. See attached picks for the difference. The top one is the PS/2 and the bottom one is S-video.
I just looked at my I-pac to confirm that it has the PS/2 lay out. I think what you need is a mail PS/2 to usb adapter or wire. You will probably bend some pins if you try to force an S-video cable in.
Both CoryBee and Fursphere links are for mail to mail PS/2 cables. It looks like yours might be a PS/2 cable as well but I just wanted to clear it all up.
Edit: I see, the seller made the mistake and you already under stand they are not the same thing.