Can a common mode choke be used at the output of an SMPS?
Can a CM choke be used at the output of SMPS supply?


Common mode chokes (in conjunction with the appropriate filter capacitors to ground) can certainly be used on the output of a SMPS: -



Picture taken from Maxim Tutorial 716 - see section entitled "Common-Mode Noise". Although not always needed (if one rail of the output is grounded), for low output noise applications they tend to be used along with a regular LC filter.