Issue
The PowerBook 540 and 520c computers will power up from a shutdown condition when any ADB device is plugged into it.
Workaround
Connect the ADB cable into the PowerBook 500 series computers at the time you plan to use the computer. When a Shut Down is performed the computer will remain powered off and will not power on automatically until the cable is disconnected and reconnected. It is the actual plugging in of the cable that causes the power on due to a power surge sensed by the PowerBook ADB port.