Cisco Catalyst 3850 Series Switches Q and A states that "Up to four switches can become part of the same Cisco StackPower stack in a ring topology".If the stack contains 5 or more members then presumeably, stackpower will continue to deliver functionality provided that I power multiple members of the stack with a gap of no more than four switches?
In this case the functionality is limited to 4 switches in the stack power due to physical limitations, if you have more then 4 then you will need to configure 2 different stack power instances.
