Electric pulses can cause failure MacFixIt reader Doug, who happens to be an electrical expert, has some explanation for why PowerBook adapters can fail when another electrical device - such as a lamp - is activated on the same circuit:
"When the lamp is turned off, or any other activity that generates a spark on the power line (motors, operating switches, plugging something in while switch on), thousands of high voltage (from 500 volts to as much as 4000 volts) pulses are generated on the power line. Each of these pulses last tens of nanoseconds with the burst of pulses lasting a fraction of a second. The pulses can come at a rate of 10 million per second! The phenomena is known as Electrical Fast Transient Burst and is covered in the international document IEC 61000-4-4.
"Unless electronic circuitry is designed to withstand this, an electronic device plugged into the same circuit may malfunction. My guess is that these pulses trip an over voltage sensor in the power module. The design fix is easy if the designer is aware of these issues and the proper steps are taken in the design of the electronic device.
"One possible help would be to put a ferrite core on the AC power cable leading to the supply (as close to the supply as possible). These can be purchased at electronic supply stores (Radio Shack) and often are called "interference suppressors" but are just powdered iron cores that snap around the cable in question. Another possibility would be to put the charger on its own surge suppressor power strip that also has "EMI" (electromagnetic interference) filtering.
Faulty adapters: Serial numbers seem irrelevant We previously noted issues with some PowerBook adapters suddenly stopping their charge flow, requiring an unplug/replug process to resume normal charging.
We initially surmised that adapters within a certain serial number range might be more prone to the flaw, but so far the data is inconclusive:
Good Serial Numbers:
Bad Serial Numbers: