Using USB Wall Outlet to Charge iPad

If your wall block was made by a reputable company then it should be just fine. For example Targus has one and I've used it with my iPad and iPod for months with no ill effect.

there is a chip in the lightning end of the cable that regulates charge and generally and usb friendly outlet will work fine

Most USB wall sockets are OK as the lightning cable has a small voltage regulator in it anyway. That said there are two caveats I would add:

1. If your home experiences a power failure, surge or brown-out, you are more likely to damage the iPad.

2. Most iPads need quite a lot of juice and you will need to make sure that the output current is enough to charge the iPad.

I always recommend that people use the supplied chargers from the original manufacturer to avoid potential issues.

You should have no issue if you stick with reputable company like Skydiver119 mentions. Also, be sure that the aftermarket charger is rated for the same output (look at the watts ratings here) as the Apple charger or higher.

It's also worth noting that using an aftermarket charger of the same wattage output as the Apple charger likely will not charge the device any faster or slower. Certainly not anything you'd notice.

Also, moving to a higher wattage charger (10 watt vs 12 watt) is fine but don't expect any noticeable vast increase in charging speed...I supposed you'd notice if you did a timed test between the two but otherwise, don't expect miracles.