Sharepoint - How to get Configuration SharePoint Database Server using Power-Shell?

Select database by type, and ask for the server. Like this:

$ConfigDB = Get-SPDatabase | Where-Object{$_.Type -eq "Configuration Database"}
$ConfigDB.server

Assuming a setup close to the defaults (and that you already loaded the SharePoint snapin via asnp *sh*), I would try this:

$server = (Get-SPDatabase | ?{$_.name -like "SharePoint_Config"})[0].Server
$server