I am typing this from a 2009 model MacBook Pro, while my wife uses my previous laptop, a PowerBook G4 circa 2002. I loved my PowerBook, but there was a fatal design flaw in the power supply. The cord that came out of it was prone to weakening and breaking off. It failed in 2008, when I did a repair like this one, cutting off the bad bits of wire and soldering the good bits back together. This held out fine for a while, until it broke at a similar place (not where I fixed it before) due to the poorly positioned wire endpoint. I tried to fix it again, but something went wrong and the power supply blew.
Of course, by this time Apple has moved on. The power supply is still available, but it’s pretty damn expensive (more than R800) and would only be here in two weeks if I ordered it today. So we went out and bought a cheap (R400) universal power adapter and spent some time researching the voltage and polarity of the G4 PowerBook power supply. For those of you wondering, it’s 24V DC with a connector just like a 3.5 mm headphone jack. The tip and sleeve aren’t connected to the power — they’re used for the light ring that indicates the status of the power. The power cord itself is positive on the ring connector and negative on the back connector.
So, after exhaustive testing to avoid frying my beloved laptop, I had a working power supply again. This is why every home should contain a multimeter and soldering equipment.