Get-EventLog -LogName System -EntryType Error | Where-Object {$_.EventID -eq 6008} | Select -Property Message | ForEach-Object { if ($_.Message -match "([0-9]{1,2}:.*[0-9]{4})") { Write-Output "System shutdown at $($Matches[1])"}}
This parses whole Event Log on the machine with level Error in System Log where the event ID is unexpected system shutdown (eventID 6008) and outputs the results using regexp for extracting the date and time:
System shutdown at 2:05:00 PM on 3/1/2019
System shutdown at 1:32:30 PM on 2/27/2019
System shutdown at 9:28:38 AM on 1/25/2019
System shutdown at 2:45:59 PM on 1/21/2019
System shutdown at 4:15:13 PM on 1/10/2019
System shutdown at 9:57:27 AM on 1/10/2019
System shutdown at 3:16:15 PM on 12/27/2018
System shutdown at 6:33:47 PM on 12/23/2018
System shutdown at 6:29:35 PM on 12/23/2018
System shutdown at 6:26:43 PM on 12/23/2018
System shutdown at 5:53:58 PM on 12/23/2018
System shutdown at 5:34:58 PM on 12/23/2018
System shutdown at 10:40:03 AM on 12/23/2018
System shutdown at 10:19:27 AM on 11/24/2018
System shutdown at 3:47:47 PM on 11/17/2018
System shutdown at 3:07:32 PM on 10/14/2018
