IEC 62684, Interoperability specifications of common external power supply (EPS) for use with data-enabled mobile telephones, is an international standard - and

IEC 62684, Interoperability specifications of common external power supply (EPS) for use with data-enabled mobile telephones, is an international standard - and is basically micro USB. Even Apple is supporting it. Some quick looking doesn't show any details of the max power rating unless you buy a copy of the spec for 45 Swiss francs.