 very slightly shorter than the ends, creating a small air gap when the core pieces are put together. This 0.28mm air gap stores the magnetic energy for the flyback transformer.
Underneath the next two layers of tape is a 17-turn winding of thin varnished wire, which I think is another shield winding to return stray interference to ground.
Underneath the shield and another two layers of tape is the 6-turn secondary output winding that is connected to the black and white wires. Note that this winding is heavy-gauge wire, since it is feeding the 1A output. Also note that the winding is triple-insulated, which is a UL safety requirement to ensure that the high voltage primary remains isolated from the output. This is one place where cheap chargers cheat - they just use regular wire instead of triple-insulated, and also skimp on the tape. The result is there's not much protecting you from high voltage if there's an insulation flaw or power surge.
Under the next double layer of tape is the 11-turn heavy gauge primary power winding, that powers the controller IC. Since this winding is on the primary side, it doesn't need to be triple insulated. It's just insulated with a thin layer of varnish.
Under the final double layer of tape is the primary input winding, which is 4 layers of approximately 23 turns each. This winding receives the high voltage input. Since the current is very low, the wire can be very thin. Because the primary has about 15 times as many turns as the secondary winding, the secondary voltage will be 1/15 the primary voltage, but 15 times the current. Thus, the transformer converts the high voltage input to low voltage, high current output.
The final picture shows all the components of the transformer; left to right shows the layers from the outside tape to the innermost winding and bobbin.
Apple's huge profit marginsI was surprised to realize how enormous Apple's profit margins must be on these chargers. These chargers sell for about $30 (if not counterfeit), but that must be almost all profit. Samsung sells a very similar cube charger for about $6-$10, which I also disassembled (and will write up details later). The Apple charger is higher quality and I estimate has about a dollar's worth of additional components inside. But it sells for $20 more.
Apple's 2008 charger safety recall
In 2008, Apple recalled the iPhone chargers due to a defect that the AC prongs could fall off the charger and get stuck in an outlet. The faulty chargers had the prongs attached with what was described as little more than glue and "wishful thinking". Apple replaced the chargers with a redesigned model indicated by the green dot marking shown above (which counterfeit chargers inevitably imitate).
I decided to see what safety improvements Apple made in the replacement charger, and compare with other similar chargers. I tried pulling out the prongs of the Apple charger, a Samsung charger, and a counterfeit charger. The counterfeit prongs came out with a tug with pliers, as there's basically nothing anchoring them but friction. The Samsung prongs took a lot of pulling and twisting with pliers, since they have little metal tabs holding them in place, but eventually they came out.
When I moved on to the Apple charger, the prongs didn't budge, even with my hardest pulling with pliers, so I got out the Dremel and ground through the case to find out what was holding the prongs. They have large metal flanges embedded in the plastic of the case, so there's no way a prong can come loose short of the destruction of the charger. The photo shows the Apple plug (note the thickness of plastic removed from the right half), the prong from the counterfeit charger held in only by friction, and the Samsung prong held in by small but sturdy metal tabs.
I'm impressed with the effort Apple put into making the charger more safe after the recall. They didn't just improve the prongs slightly to make them more secure; clearly someone was told to do whatever it takes to make sure there's absolutely no way the prongs could possibly come loose again under any ci