Which capacitor to change on CR-10S S500 motherboard?
You are looking for a capacitor that must be connected to Pin 4 of the LM2596.

Maybe you could provide a better picture of that area so we could see the different tracks on the board.

The LM2596 is in the center of the right side of the board (it is also labeled  with LM2596D). The pins should be counted from top to bottom (in your picture)

My guess is, the Elko you are looking for is connected to C31, and you must look for the positive pin.



In this wiring diagram Cout is the capacitor you are looking for. The SMD Parts R1, R2 and CFF should be R31, R32 and C31 in your picture.

With the corresponging measurements I would say you do not need to replace the capacitors. 

In comparison to the old board your board already has the "fix" implemented.