The method by which your server proves control to the CA that it controls power-forums.com. Previously Certbot used a different method, TLS-SNI-01, which was later disabled, so now you are left with either HTTP-01 or DNS-01.
As written in the post, update your Certbot to a newer version, and it should automatically deal with renewal.
That's not going to work, because wildcards are only available by DNS-01 (which requires automatically or manually adding TXT records to your domain's DNS).
Are you sure you need a wildcard? Based on your previous certificates, it wouldn't seem that way.
If you only need [power-forums.com www.power-forums.com], perhaps you can try:
certbot certonly --preferred-challenges http -d www.power-forums.com -d power-forums.com -w /var/www/acme/