Powershell in Kali Linux 2018.3 currently requires libcurl3 to run. However, Kali is currently using libcurl4.

Other programs are currently using libcurl4 and if you downgrade to libcurl3 multiple programs including Metasploit also break as well.

Proof:
root@kali:~# apt -y install powershell
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
powershell : Depends: libcurl3 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

root@kali:~# apt-get install libcurl3
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
curl libcurl4 metasploit-framework
The following NEW packages will be installed:
libcurl3
0 upgraded, 1 newly installed, 3 to remove and 0 not upgraded.
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After this operation, 250 MB disk space will be freed.