To what extent are all USB chargers, devIces and sockets etc all compatible? I just bought an iPad and connected it to my iPhone charger, but thought it was charging slowly. On checking the iPad charger it is 5.2V x 2.4A and the iPhone one is 5V x 1A. If the iPad is connected to the small charger does it just charge slower or does it overload it? If the iPhone is connected to the large charger does it just use less current than available? I’ve never used wall sockets with built-in USB ports. What happens if the total load of all the devices plugged in exceeds their rating?