RT / 2
24W (12V / 2A)
Pro / Pro 2
48W (12V / 4A)
Both the original RT/ RT2 charger and the newer Surface Pro chargers can be used on the RT and RT2, but the newer ones will not charge faster.
Good link explaining the various differences between the Surface platform PSU's https://dancharblog.wordpress.com/2016/12/10/surface-book-pro-3-pro-4-and-docking-station-power-supplies/
If the LED light on your Surface charger is blinking, flashing, off, or on (but your Surface still isn’t charging), here’s what to do:
Disconnect the charger from your Surface, unplug the power cable from the electrical outlet in the wall, and then disconnect any USB accessories. Wait 10 seconds. After that, clean everything with a soft cloth, and check for any damage. (Be sure to replace damaged cables.) Plug the charger back into the electrical outlet and your Surface.
Note: After you unplug the charger from your Surface and the wall, make sure to wait 10 seconds. This step resets the charger.
Flip the charger 180 degrees, and check to see if the LED light comes on and if your Surface starts charging again.