After quite some hacking I now longer get a warning from a package, did I have success? How do I list all loaded packages? (NOT INSTALLED, installation was not the problem, loading was, eg require).
As far as I remember, the function
package-activated-list is what you are looking.
Source: A Reddit thread (retrieved today, 2018-08-28)
I personally use Paradox package manager. With paradox loaded,
M-x paradox-list-packages shows new, available, installed, built-in, obsolete and incompatible packages. Just scroll through the list to see what's up.
Additionally, Paradox is a really slick package manager, allowing you to upgrade available packages, delete packages that have been installed and many, many more useful tasks.