Ok its confusing but Ill try and explain what I see. All the powerbooks seem to list wattage from 15 to 19 watts. Only issue is every single powerbook AC adapter listed all say 7.5 volts X 2.0A. For every model of 1XX powerbook of the square design. Even the one listed for 17 watt and 19 watt say 7.5V X 2.0A. As for safe under powering will usually not let a computer power on, so I guess that could be an issue but shouldn't hurt anything. Weird this had not been noticed or mentioned till now.