Comment 3 for bug 1829197

Hi, at least as of today this seems to match well:

root@x:~# apt-cache policy postgresql-9.5
postgresql-9.5:
  Installed: 9.5.19-0ubuntu0.16.04.1
  Candidate: 9.5.19-0ubuntu0.16.04.1
  Version table:
 *** 9.5.19-0ubuntu0.16.04.1 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        100 /var/lib/dpkg/status
     9.5.2-1 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages

And the changelog is on 9.5.19
root@x:~# zcat /usr/share/doc/postgresql-9.5/changelog.Debian.gz | head
postgresql-9.5 (9.5.19-0ubuntu0.16.04.1) xenial-security; urgency=medium

  * SECURITY UPDATE: New upstream release (LP: #1839058)
    - Require schema qualification to cast to a temporary type when using
      functional cast syntax (CVE-2019-10208)
    - Fix failure of ALTER TABLE ... ALTER COLUMN TYPE when altering multiple
      columns' types in one command. This fixes a regression introduced in the
      most recent minor releases
    - Details about these and many further changes can be found at:
      https://www.postgresql.org/docs/9.5/static/release-9-5-19.html

You listed:
postgresql-11 (11.2-1.pgdg14.04+1) trusty-pgdg

That never existed in the Ubuntu archive.
It is most likely that you installed from upstreams PPA at https://wiki.postgresql.org/wiki/Apt
They produce such versions and it most likely is a conflict or remainder of that.

You'd need to clear out all non-Ubuntu-Archive packages to resolve this, as it isn't a Ubuntu packager there isn't much Ubuntu can do about it :-/