What cable do I need?

So, before coming over to SE Asia, I'd found a "new" GPS unit to use as a backup to my "old" GPS unit. In reality, both are older Garmin models, one a GPS 12, and the other a GPS 12XL, very nearly identical, and the price was right on the 12XL, only $55 in a pawn shop. I like having a GPS with me when I travel for a few reasons, one, it helps me find my way around, two, it gives me something tangible to bring back with me after my trip so I can say "I was there", and three, it gives me something to do while on boring road trips, like the bus route from SG to KL. Five hours of listening to a bus drone on while driving through rubber plantations on a freeway that's as boring as any in the US gets pretty old pretty fast, especially if it's at night and you can't see much anyway.

Anyway, I was talking to my friend Chris, and he gave me a link to a freeware chartplotter software package, but I'd need a cable for the GPS units to talk to my computers. While searching for a cable online, I ran across a page called Pfranc, which is a site created by a guy in Oregon who sells data/power cables that he makes himself. I found a guy who'd franchised for Washington State, but decided to look in Singapore & Malaysia just for fun. Turns out there's a guy in Singapore, Daniel Mok, who makes and sells the cables as well. I contacted him, telling him that we'd be there last week, and could I buy a cable from him. No problem. After some exchanges of email explaining what I needed (I thought), then several phone calls between my brother in law Sun & Daniel, we met up with him to purchase the cable. Got back to Sun's apartment, and the cable didn't fit. Turns out that there is a voltage difference between the two GPS units, which doesn't make sense to me, as they both run off of 4-AA batteries, but apparently the 12 runs off of 5-8 VDC, and the 12xl runs off of line voltage, 12 VDC. Both plug into the cigarette lighter in your car or boat, but one runs at a lower power, and the other higher. The higher power cable is blocked by a pin in the center of the plug on the GPS so you can't plug it in. Of course, this is the one I have with me, so the cable I'd gotten wouldn't work with the GPS I have for this trip. And of course I found this out the evening before we were leaving for KL, so there was no way to make an exchange. I wrote to Daniel explaining my predicament, so he called Sun, asking about the exchange. This created a fire storm of SMS messages going back and forth from SG to KL, I think all the female members of my sister in law's family got at least one message from Sun, asking me for clarifications. Mostly while I was swimming in the pool with the boys. Eventually it was ironed out, and I will end up with two cables for less than the price of one in the US.