Thanks Head on a Stick,

That was very useful. As an additional note...

On my Dell XPS 13 I also had to check the contents of /sys/power/mem_sleep as the default (between brackets) was s2idle and it indicated that also 'deep' or suspend to RAM was possible, saving even more power.

I followed the instructions of https://www.kernel.org/doc/html/v4.18/a … tates.html to make 'deep' the default by adding it to /etc/default/grub e.g.

GRUB_CMDLINE_LINUX_DEFAULT="quiet mem_sleep_default=deep"

and ran 'update-grub' afterwards.