Add Site Collection Administrator to All Sites in SharePoint using PowerShell

Site collection administrators have God like power within a Site Collection in SharePoint 2016. Apart from Primary & Secondary site collection administrators, we can add additional site collection administrator on any SharePoint site collection.

How to Add a Site Collection Administrator in SharePoint 2016?
To Add a Site Collection Administrator follow these steps:

• Site Settings Gear >> Click on "Site Settings" Menu Item
• Click on "Site collection administrators link under "Users and Permissions"
• Enter the New user in Site Collection Administrators Field. Click OK to save your changes.
  

OK! Now, How about adding a same user as administrator in all site collections?

PowerShell Script to Add a Site Collection Administrator to All Site Collections in SharePoint:

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#User Account to add as Site Collection Admin
$UserAccount="Crescent\Salaudeen"

Get-SPSite -Limit "All" | ForEach-Object { 
$User = $_.RootWeb.EnsureUser($UserAccount)
    if($User.IsSiteAdmin -ne $True)
    {
        $User.IsSiteAdmin = $True
        $User.Update()
        Write-Host "Added Site Collection Administrator for Site Collection:" $_.URL -ForegroundColor Green
    }
    else
    {
        Write-Host "User is already an Site Collection Administrator for Site Collection:" $_.URL -ForegroundColor Yellow
    }
} 

You can use Web Application User Policy in Central Admin to give Full control to the Entire web application, instead of adding users into individual site collections!