To anyone trying to add PowerCMS to their site in the 2020s or later.... Here's a helpful tip.
I have spent a lot of time trying to get past the step 4 of 5 (setting the admin login) and finally found the solution. It kept telling me that it couldn't save my information and to check my database connection. I have been trying all the solutions in these help forums, and here is what worked. Most of the forum answers are from long ago, before there was the MYSQLI option. Apparently PowerCMS was never updated for that connection so you need to use the classic MySql connection.
Here's the thread with the solution: https://www.webassist.com/forums/posts.php?id=41218
Here's Ray's comment from 2018 from that thread:
We debugged this in a screen sharing session. The issue was that a MySQLi connection was specified and PowerCMS has not been updated for MySQLi yet. We updated the connection to standard MySQL and the installer was able to complete.
Good luck!