Snubber circuit

Snubber circuit is used to control the voltage stress across power MOSFET and power Diode. Without snubber, MOSFET or diode can be blew up due to the high volateg stress, so it is very important for power supply design. The snubber circuit normally can not affect the output regulation, since it is more related to feedback loop.

I forgot to mention that snubber is vey important for EMI design too.

Thanks replies. Exactly I want to learn how snubber circuit affects feedback. For example does wrong snubber circuit affect feedback wrongly? 

The snubber circuit has no effect for output voltage if close loop is used to regulate the output. However in your circuit, one is controlled with secondary zenner , and another channel is open loop. So the snubber circuit will affect the uncontrolled output a little bit. As you know, the output diode can not coduct immediatley because of the forward recovery of the diode,  the enegy in the flyback transformer can be transferred to the output through the snubber during the forward recovery time, so the output will be slight higher with the snubber circuit.