Is it harmfull for the iphone 6s to charge it by non apple power bank case?

Is it harmfull for the iphone 6s to charge it by non apple power bank case?

Added (1). i mean should i use the apple power bank case or it is okay to use any power bank case?

Should be.
Get the volts & amps to compare.
You don't want to cook your mobile, nor not adequately charge it.

Any USB port built to serve enough power will do. My phone charges fastest in the car, even faster than the official iPhone or iPad chargers.