How can a USB charger with USB-A connector handle 3 Ampere?
Technically speaking, the USB PD (power delivery) specifications do define special "USB 3.1 PD Connectors", including Type-A style. This was before the Type-C connector was introduced. The connectors have additional contacts to detect cable insertions. The connectors are supposed to carry up to 5A with contact overheat of 30 deg.C over ambient (25 deg.C). Same goes for the 3A-rated connectors, see Section 3.6.5.1 of USB Power Delivery specifications. So the 55 deg.C on the connector seems to be within specifications, which should be painful to the touch.

However, I myself have never seen these connectors, and I have a suspicion that no one manufacturers them in reality. All regular USB Type-A connectors have typical contact rating of 1.5A, and only few (typically of odd up-right shape type mount) have rating of 2.5A. Of course, a wall charger can advertize whatever they wish, or you might be a lucky one to see the unique "PD connector".