Below script to add a group to full control access to all the web-applications in SharePoint farm.
PowerShell
$userOrGroup = "domain\ROL-G-All-SharePointAdmin-Admin"
$displayName = "SharePoint Team"
Get-SPWebApplication | foreach {
$webApp = $_
$policy = $webApp.Policies.Add($userOrGroup, $displayName)
$policyRole = $webApp.PolicyRoles.GetSpecialRole([Microsoft.SharePoint.Administration.SPPolicyRoleType]::FullControl)
$policy.PolicyRoleBindings.Add($policyRole)
$webApp.Update()
}