You should be able to get a good idea by looking at the AC power brick for the computer. I just looked at the one for my old IBM ThinkPad 600E, and its output is listed as 16V / 3.36A. Multiply the voltage and current to get power, and that gives us 53.76 Watts. I'd guess you'd be fine with the 100W model, but double-check the math if you want to be sure.