Back to the Original post, if you're still interested, Alan, I reckon the 5vA is supposed to be 5VA which is approximately equivalent to 5Watts ie 1A at 5V.
Nice find, DT. Some of those plug in USB outlets are very low current and not much use for charging. 2A+ is a nice healthy one. Of course, with the outlet plugged into the waterproof socket and a cable stuck into that, it won't be waterproof any more.
I'd be inclined to go for the Garmin lead with its integral 12V to 5V converter hooked up to the connector under the nose cone.