$offset = ([System.TimeZoneInfo]::Local).BaseUtcOffset.ToString()
$offset = $offset.Substring(0,$offset.LastIndexOf(':'))
$date.ToString("yyyy-MM-ddTHH:mm:ss.fff") + $offset
Format a DateTime value in the ISO8601 format
PS C:\> $Date = Get-Date >> $offset = ([System.TimeZoneInfo]::Local).BaseUtcOffset.ToString() >> $offset = $offset.Substring(0,$offset.LastIndexOf(':')) >> $date.ToString("yyyy-MM-ddTHH:mm:ss.fff") + $offset 2019-03-28T11:06:01.608-06:00