I wrote 3 simple scripts to get, add or remove site collection administrators.
Get Site Collection Administrators:
This script will run through every site collection on a web application (as long as you have the permission for that) and store the list of all site collection administrators in a .txt.
Add Site Collection Administrators:
This script will add users from an array to all site collections as admins. The result will be stored in a .txt.
Remove Site Collection Administrators:
This script will remove admins from all site collections. The result will be stored in a .txt.