How do i fix this switching power supply if the ampere drop from 12.5a to 0.90a
Is there any other way to fix this problem?? Thanks in advance.

 

You'll need to explain the problem a bit better. If you are looking at short circuit current, the lower value might be normal if the supply has foldback current limiting.

What kind of load are you trying to drive? How do you know the PS is not delivering the higher current?