Verified 1.1ubuntu1.18.04.7~16.04.3 on Xenial:

root@x-lp-1823872:~# cat acpid.equivs 
Source: acpid
Section: misc
Priority: optional
Standards-Version: 3.9.2

Package: acpid
File: /etc/acpi/events/powerbtn/powerbtn 
 # /etc/acpi/events/powerbtn
 # This is called when the user presses the power button and calls
 # /etc/acpi/powerbtn.sh for further processing.
 .
 # Optionally you can specify the placeholder %e. It will pass
 # through the whole kernel event message to the program you've
 # specified.
 .
 # We need to react on "button power.*" and "button/power.*" because
 # of kernel changes.
 .
 event=button[ /]power
 action=/etc/acpi/powerbtn.sh
root@x-lp-1823872:~# equivs-build acpid.equivs 
...
root@x-lp-1823872:~# dpkg -i acpid_1.0_all.deb 
dpkg: warning: downgrading acpid from 1:2.0.26-1ubuntu2 to 1.0
(Reading database ... 32148 files and directories currently installed.)
Preparing to unpack acpid_1.0_all.deb ...
Unpacking acpid (1.0) over (1:2.0.26-1ubuntu2) ...
Setting up acpid (1.0) ...
Processing triggers for man-db (2.7.5-1) ...
root@x-lp-1823872:~# dpkg -l unattended-upgrades | cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                Version                    Architecture Description
+++-===================-==========================-============-===========================================
ii  unattended-upgrades 1.1ubuntu1.18.04.7~16.04.2 all          automatic installation of security upgrades
root@x-lp-1823872:~# unattended-upgrade --dry-run 
Traceback (most recent call last):
  File "/usr/bin/unattended-upgrade", line 1998, in <module>
    sys.exit(main(options))
  File "/usr/bin/unattended-upgrade", line 1714, in main
    if conffile_prompt(item.destfile):
  File "/usr/bin/unattended-upgrade", line 929, in conffile_prompt
    with open(prefix + conf_file, 'rb') as fp:
IsADirectoryError: [Errno 21] Is a directory: '/etc/acpi/events/powerbtn'
root@x-lp-1823872:~# apt install -y -qq unattended-upgrades 
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
Suggested packages:
  bsd-mailx default-mta | mail-transport-agent needrestart
The following packages will be upgraded:
  unattended-upgrades
1 upgraded, 0 newly installed, 0 to remove and 9 not upgraded.
Need to get 41.4 kB of archives.
After this operation, 8,192 B of additional disk space will be used.
Preconfiguring packages ...
(Reading database ... 32136 files and directories currently installed.)
Preparing to unpack .../unattended-upgrades_1.1ubuntu1.18.04.7~16.04.3_all.deb ...
Unpacking unattended-upgrades (1.1ubuntu1.18.04.7~16.04.3) over (1.1ubuntu1.18.04.7~16.04.2) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for ureadahead (0.100.0-19.1) ...
Processing triggers for systemd (229-4ubuntu21.21) ...
Setting up unattended-upgrades (1.1ubuntu1.18.04.7~16.04.3) ...
root@x-lp-1823872:~# unattended-upgrade --dry-run --verbose
Initial blacklisted packages: 
Initial whitelisted packages: 
Starting unattended upgrades script
Allowed origins are: o=Ubuntu,a=xenial, o=Ubuntu,a=xenial-security, o=UbuntuESM,a=xenial
Option --dry-run given, *not* performing real actions
Packages that will be upgraded: acpid
Writing dpkg log to /var/log/unattended-upgrades/unattended-upgrades-dpkg.log
/usr/bin/dpkg --status-fd 9 --unpack --auto-deconfigure /var/cache/apt/archives/acpid_1%3a2.0.26-1ubuntu2_amd64.deb 
/usr/bin/dpkg --status-fd 11 --configure acpid:amd64 
/usr/bin/dpkg --status-fd 13 --configure --pending 
All upgrades installed
#