How much load can these plastic cabinet things hold?
If they are like mine I would say over 100 lbs the pin is very strong, I have found the particle board to crumble or shelf break before the pin gave way , the ones that hold in place with the clips are great as they cannot fall out. There should be 4 pins  2 in each side.

Is that shelf in backwards? Mine the front of the shelf has a piece of laminate over the particle board.