Cold cathode lights take very little power so your current draw will be low. Don't know the exact figure for that light but others of similar size take 5 ma. at approx 700v.
Here is an analysis of the power draw with a 12V supply found on Toms Hardware.
"These guys work, as you probably have figured out, by taking your 12V supply and jacking it up to a high voltage (and lower current) to run the lamp.
Any 12V DC supply should work, and probably a few volts above or below. An important thing is how much power you need. I would assume the 5mA is the inverter output, not the input. I know these lamps take around 2-5W, depending on size, so that sounds right: 680V x .005A = 3.4W
Then you figure how much current that ends up on the 12V side: 3.4W / 12V = .283A or 283mA. Add in some extra current to account for efficency, (the inverter will be anywhere from 60-90% depending on the design) and you're looking at around 500mA for the 12V supply.
Lots of wall warts are available in that range. I'd give that size a shot, and measure the voltage when you fire it up. If it dosen't drop more than a few volts, you should be fine. Inverters aren't very critical on input voltage."
Hope that helps