Current configuration has

xss-lock --session="$XDG_SESSION_ID" --ignore-sleep --notifier=screenlock-notifier --transfer-sleep-lock -- locker.sh

where screenlock-notifier provides dimming and other logic.
locker.sh switches the screens off via xset dpms force off and launches xsecurelock:

xset dpms force off
/usr/bin/env XSECURELOCK_SAVER=saver_blank \
 XSECURELOCK_AUTH_TIMEOUT=5 \
 xsecurelock

Now when input is registered, display wakes up and auth screen is shown. If no login happens in XSECURELOCK_AUTH_TIMEOUT, the display is blanked, but not switched off as it was right upon locking.

How to make sure screens are turned off again whilst locked?

Adding XSECURELOCK_BLANK_DPMS_STATE=off env var makes no difference either, tried also {suspend,standby} values.

running ver 1.9.0