I'd like to add the following information with regards to charger ratings in relation to the topic at hand:
The values that you can find printed on the body of the charger are values that are guaranteed by the manufacturer to work with the intended device. Values that can be found are wattage (abbreviated unit - W), voltage (abbreviated unit - V), sometimes current (given in amperes - A, or sometimes given in milliamperes - mA).
How do we interpret this? This means any device can be charge by the charger provided it will not draw more than the indicated amperes at the specified voltage or the device will not use up energy more than the indicated value at the specified voltage.
With regard to devices in particular the Ipad 3 it is generally not known how much current or energy it is drawing from the battery. But when the battery is fully discharged and it is charged by the charger, it is guaranteed by Apple that the current or energy provided by the charger is enough to restore the battery to full charged condition at the specified time and under no operation condition. Does this mean that the Ipad is drawing 2A while being charge? It is drawing that amount for a certain period of time only, usually at the initial condition of charging. Probably, at 50% battery charged condition the ipad is drawing only 1A or less compared to the initial condition of 2A. Current or energy drawn by the battery at full charged condition will approach a negligible value as charging time goes on. Operating the Ipad while being charged causes an overloading condition at the initial charging condition granting that the Ipad will really draw 2A. So IMO the Ipad can be operated while being charge without fear of overloading the charger when the battery charged condition is at 50% or more.