I have several power adapters that have USB connectors, and was wondering if they were usable with the A1. The adapter from Lenovo is rated at 5.0 amps. I have one that is rated 5.5 amps, one that is rated 5.0, and one (which uses disposable AA batteries) for emergency use rated at 3.0 amps. I'm pretty certain that the 3.0 amp and 5.0 amp adapters are all right to be used, but I am not certain about the 5.5 amp adapter.
Officially, Lenovo can only recommend use of the adapter that came with the A1 as it is tested. Generally, the current rating is simply the maximum capability of the power supply. The actual current draw depends on the internal demand of the device (your A1). If the adapter that comes with the A1 is rated at 5 amp, then it is more than likely the actual draw is somewhat less. So the 5.5 amp adapter should be fine but the three-amp adapter may overheat as the device tries to draw more current than the adapter is rated for, or the A1 may not properly charge, could shut down, or otherwise malfunction if not supplied with the required voltage and current.