Over the last few years, I've experimented with numerous charge/sync cables for my iPhone 4S and iPad 2. Cable quality varies widely, so take a good look at the cable and connector construction before you buy.
Knockoff cable makers have found many ways to cut costs. With careful inspection, you can spot the differences. Take a look at a genuine Apple 30-pin connector (right) vs. the knockoff (left) in Figure 1. The genuine Apple cable on the right has a thicker cable. If you gently pull on the cables, you'll find that the Apple cable has far better strain relief. Also note the sight differences in the marking. The lines on the real Apple connector's marking are slightly heavier.
Figure 1. Which is the genuine Apple 30-pin connector?
Things get more interesting when you look inside at the pins on the 30-pin connectors. Figure 2 shows the Apple cable while Figure 3 shows the knockoff cable.
Figure 2. A close-up of a genuine Apple 30- pin connector shows the pins Apple uses for power and USB data.
Figure 3. A fake Apple connector uses four pins instead of six, two fewer returns (GND).
Note the difference in the number of pins used in the Apple and in the fake. The Apple connector uses pins 1, 15, 16 (all GND), plus pin 23 (USB +5 V), pin 25 USB data -) and pin 27 (USB data +). The fake has only one GND connection on Pin 16. It works but is more likely to fail with only one return line.
Some charge/sync cables for Apple devices are clearly third party. Often they aren't white, meaning the manufacturers don't try to pass them off as genuine. For example, Dynex cables come in many colors. I bought two at Best Buy a few months ago and I like them For one thing, the 30-pin connectors fit my iPhone and iPad well, as do the Apple cables. Some fake cables are either too loose or too tight when you mate then to your device.
In Figure 4, you can see the Apple (white) and Dynex (blue) 30-pin connectors. What's this, the blue Dynex connector uses more pins than the Apple connector. It adds pins 19 and 20 (Firewire +12 V), and pin 21 (accessory indicator). It doesn't use Pin 15 (GND), but it adds pin 11, designated as Serial GND on this pinout chart. Why would Dynex use pin 11 instead of pin 15? I'll have to study the differences. If you know, please leave a comment and tell us.
Figure 4. The blue Dynex connector uses more pins than Apple. They are for Firewire +12 V and accessories, but why?
There are many ways that manufacturers can cheapen their fake cables. While some are visible -- thin cables, fewer pins, cheap housings, poor fits -- some require a test. In the video below, I check continuity between the 30-pin connector metal shield and the USB connector shield. Guess what? The shields are electrically connected in the genuine Apple and name-brand cables, but not the fakes. That means the fake cables have no EMI protection and only one return line for the power, but they work.
Then there are the fake Apple chargers, a story for another day.
A fake Apple charger shows poor assembly practices.