I don't think you should be focused on the 5 volt issue, that's the common standard for USB 2.0 voltage. It's current, amperage, that's the differing number between devices. Also, most adapters have pretty crappy regulators in them so if you check them with a multi-meter you'll will very rarely come across one that puts out exactly 5 volts (understandable considering most wall worts are relatively tiny, there just isn't enough space to pack in the proper amount of circuity components to filter the output to an exact amount).
Anyway, USB 2.0 cables have at least four wires in them -- Android uses two for power and two for data. Apple doesn't follow the common industry standards and so on a typical Apple cable there will be the common USB plug end but on the other side is their proprietary plug end (applicable to before Apple's recent change to USB 3.1/type-C). The two and two, power and data, configuration that Android phones rely on doesn't apply to Apple chargers. Most Android devices null out those two data connections when they sense non-data signals coming through so you can still at least charge up your phone off off an Apple charger, but in your case it just sounds like something got messed up. Did you remove your battery and just let your phone sit there a few minutes before putting it back together again?