Here's a short one.  We want to know when this box was last rebooted.  Sure, it's in the SCOM DB, but this is probably faster. The Win32_OperatingSystem WMI object contains the LastBootupTime attribute.  Beyond that, it's a simple matter of converting that from WMI-time to [datetime]$time.

And, because computers may be in the middle of rebooting right now, they might not be pingable., hence the simple ping test.

 

function Get-LastRebootTime {
     param ( 
         [Parameter( 
             Position = 0,  
             ValueFromPipeline = $true
             ValueFromPipelineByPropertyName = $true 
         )][String[]]$ComputerName = @($env:COMPUTERNAME),
         [int]$Timeout = 1000
     );
    
     begin { 
         $wmi = New-Object WMI; 
         $ping = New-Object system.net.NetworkInformation.Ping;
     }
    
     process {
         foreach ($computer in $ComputerName) {
             $object = $true | select -Property Name, Rebooted;
             $object.Name = $computer.ToLower();
             if ($ping.Send($computer, $Timeout).Status -eq 'Success') {
                 $object.Rebooted = $wmi.converttodatetime((Get-wmiobject -computer $computer win32_OperatingSystem -ErrorAction SilentlyContinue).lastbootuptime);
             } else {
                 $object.Rebooted = "NoPing"
             }
             $object;
         }
     }
}