AC mains current and transformer current

These are two separate issues:

1) How much current the transformer can supply?
2) How much current can your mains AC supply deliver?

The answer to (2) is easy. Go to your fuse box and look at the rating on the fuse or circuit breaker.
If the rating is 40A, then the maximum power delivered before blowing the fuse is 220V x 40A = 8800W.

Generally it is between (20A-50A)

and the answer to (1) is,

The maximum current delivered by the transformer will depend on the size and construction of the transformer:

1. As an example, let us say the transformer steps down from 220VAC to 20VAC.
    This is approximately 10:1 reduction.

2. Then if the transformer is rated at 1A on the secondary, the primary will take 0.1A.
3. That is, power in is equal to power out for a 100% efficient transformer.

The power pole outside your house, that big round
thing is a ~400 amp transformer :-)

Reference:
forum.allaboutcircuits.com/showthread.php?t=78464