What is missing is the duration for which the transformer can supply the rated amps without over heating. Door bell transformers only supply the load while the bell push is pressed and then only for a few seconds. This allows the design to use minimum wire size. They depend on the thermal mass of transformer to be able to cope with the heat produced in the wire for a few seconds. If the bell was ringing for a long time the average bell transformer will over heat.Seriously? Amps don't mean the same thing between companies ?
The manufacturers do rely on some customers being un-aware of some information about their transformers.Is there some amp conspiracy that means anyone without huge amounts of knowledge is destined to fail at wiring doorbells?