Have tested charging my 2a. Using a USB tester (battery guru reports 5w less than my USB tester) , i get peaks of 42w charging. My charger is just a simple 100w charger with PD3.0. When the phone was new, it would only charge at 28w max, but after a few cycles - it charges at faster speeds. Charging 50% takes about 30mins. My charging is set to 80% (custom charging mode not smart charging) and the room temperature is 25-27c.
update: After using my phone outside in 45c heat, charging was only 10w when i got home. After cooling the phone, charging started at 42w before tailing off. More of an FYI than probable cause for other peoples slow charging.