I think I have a different problem.
Now even when the cable is plugged out, it only rarely suspends.

I tried 

--8<---------------cut here---------------start------------->8---
(elogind-service-type config =>
                           (elogind-configuration
                            (inherit config)
                            (handle-lid-switch-external-power 'suspend)))
--8<---------------cut here---------------end--------------->8---

and rebooted, but it does not seem to make a difference.

Something's fishy...

-- 
Pierre Neidhardt
https://ambrevar.xyz/