Get-TimeZone.ps1

function Get-TimeZone
{
    [CmdletBinding()]
    param()

    Write-Verbose -Message ($LocalizedData.GettingTimezoneCimMessage)

    $TimeZone = (Get-CimInstance `
        -ClassName WIN32_Timezone `
        -Namespace root\cimv2).StandardName

    Write-Verbose -Message ($LocalizedData.CurrentTimezoneMessage `
        -f $Timezone)

    return $TimeZone
}

Get-TimeZoneId.ps1

function Get-TimeZoneId
{
    [CmdletBinding()]
    param(
        [Parameter(Mandatory = $true)]
        [System.String]
        $TimeZone
    )
    # Convert TimeZone Standard Name to TimeZone Id
    $timeZoneInfo = [System.TimeZoneInfo]::GetSystemTimeZones() |
        Where-Object StandardName -eq $TimeZone

    return $timeZoneInfo.Id
}