By Werner Ruotsalainen updated on 07/26/2012
UPDATE (07/26/2012): at last a cheap ($3) Chinese cable that is actually worth paying for (if you do want to recharge your iPad with it - again, for iPhone / iPod touch recharging, generally, any cable will do)!
The description of the double charger cable ("New 2in1 USB Charger Cable Cord For iPhone 3 4GS iPad iPod Samsung/HTC/Motorola") HERE states the following: "Thick cable power wires, supporting fast charging (2A)". I've measured its electrical characteristics. Well, this time, with this cable, the specifications were spot on: it's indeed charging the iPad with 2.1 Ampers. (It's also capable of synchronizing, of course.) That is, this is the first Chinese cable I recommend if you look for something cheap but still capable (and also capable of recharging micro USB devices).
UPDATE (07/22/2012): 1, THIS article elaborates on the quality and the inner structure of Apple's chargers (thanks, Özgün Can Özgüneş!)
2, I've tested the charging Amperage of the older (A1388) HDMI adapter (Apple Digital AV Adapter), which also has a sync socket for recharging while using the HDMI output. It's about 1.98A; that is, about 120 mA less than without the charger. This means you'll don't want to let the adapter in and route the charger through it if you want the fastest recharging possible. (I'll soon test the newer model - MD098ZM - too.)
UPDATE (07/08/2012): 1, I've also tested THIS ("USB Data Cable for iPhone 4 - White (100cm-Length)") cable. About 1Ampers, that is, really bad quality; probably this is why not only iPads but also iPhones very frequently display the "This cable can't charge" message. Not only my iDevices but also some of the people that commented on the item. Having gone through some of them and having been continuously facing this message with almost all of them, I need to state this cable is absolutely rubbish. You indeed get what you pay for...
2. As has already been elaborated on in the comment section below, I've also thoroughly tested the data transfer speed of third-party (cheap) Chinese cables. I've decided to elaborate on it in a separate article. Please see THIS article.
3. Speaking of the questions asked in reader comments, let me emphasize: if you're looking for an iPhone recharger or for a cable to be used with only an iPhone charger (1 Ampers max.), even the worst-delivering cable (like the cheap 10 feet one) will do. (Of course not the one I've just described in Bullet 1 above. It very frequently refuses to work even with iPhones.) The discussion only applies to the iPad with its massive 2-Amper recharger and highly elevated cable quality needs.
You may have found the cables supplied (and, in the Apple Store, sold - LINK) with Apple's iDevices are fragile, short and expensive. At least I did and, consequently, purchased quite a few third-party one. In the article below, I report on my measurements.
I've made some serious tests to find out which cables I should use to charge my iPad 3 as quickly as possible. During my tests, I've found that, even though Apple's own, long, high-quality Component Cable uses a much thicker USB wire than Apple's default, short charger, it's still incapable of matching the same Amperage. Maybe this is the reason Apple doesn't manufacture longer cables in its store, after all.
The results speak for themselves: there is simply no point in using non-Apple-manufactured, cheap cables. Not even the shortest one of them could supply the iPad 3 with more than 1.5A's, with the 10 feet one delivering even less.
All in all, if you really need every single electron Apple's iPad charger can provide, stick with Apple's default cable and even prefer it to Apple's other, longer cables (composite / component) with also recharging functionality. It's on the AC side that you should add an extender (longer cable) - there, even the cheapest cable will do. (Of course, using a charger so close to the iPad may be pretty inconvenient in cases. Nevertheless, at least the iPad will, then, be fed with the nominal 2.1 Ampers.)
Note that this doesn't necessarily mean all third-party, cheap and/or long cables are bad, just that the ones I've tested have turned out to be insufficient. For example, I don't think the (expensive) third-party cables (for example, that of Griffin) really can't deliver the advertised 2.1A. (Actually, the just-linked 10-foot Griffin cable does state it does deliver 2.1A because of the thick wires it contains. These thick wires may also be cause for it having received a lot of “It wont stay connected to either my iPhone, iPad or iPod” type of comments.)
And, finally, let me point out that you in no way should purchase aftermarket, cheap (=Chinese) iPad rechargers. While they promise 2A current, they, in general, are far worse. Cables like composite cables and adapters like X-in-one SD / USB / Camera Connection Kit knock-offs also belong to this "never ever" category (except if you only plan to use the composite cable on jailbroken devices, together with Resupported 4): all(!) of the Chinese cheap knock-offs I've tested were useless, even the more expensive ones. Some of them were refused right away, some others "only" after some 1-2 minutes, which also meant I've never been able to import any longer video to my iPad. Go for the original Camera Connection Kit, it's cheap and does work.
All genuine Apple cables coming with both iPhones and iPads: 2.1A
Apple's own Component Cable (LINK - not the composite one!): 1.8A
Aftermarket (non-Apple, non-chipped and, therefore, needing Resupported 4) composite video cable (LINK): 1A
Cheap 3m / 10 ft cables like THIS: 1.3A
Aftermarket “USB Charging Cable for All iPod (100CM-Length)” cable (Google cache link): 1.5A