Cascaded SMPS's and instability?

Hello,
If an offline 160W SMPS provides an output voltage rail that is used as an input voltage rail for a switch mode buck led driver, then could this cause instability , due to an interaction between the feedback loops of each smps converter?

To solve this instability, do we have to ensure that the feedback loop bandwidth of the upstream smps must be at least three times greater than that of the downstream smps?

Yes, it can cause instability. Especially if the power drawn is typically more than about 66% of the rated capacity, or if the loads are transient in nature. The damping factor of the voltage control loop plays an important role.
There are ways to take care of this, normally on a case to case basis.

Ramesh