DateTime to ISO8601

$offset = ([System.TimeZoneInfo]::Local).BaseUtcOffset.ToString()
$offset = $offset.Substring(0,$offset.LastIndexOf(':'))
$date.ToString("yyyy-MM-ddTHH:mm:ss.fff") + $offset
Details
Format a DateTime value in the ISO8601 format

Example
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
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