Just a quick post and a day late for #SQLNewBlogger There are some excellent posts on that hashtag and I recommend that you read them

When you know a server name but not the name of the instances or the ports that they are using this function will be of use

<#
.SYNOPSIS
Shows the Instances and the Port Numbers on a SQL Server
.DESCRIPTION
This function will show the Instances and the Port Numbers on a SQL Server using WMI
.PARAMETER Server
The Server Name
.EXAMPLE
Get-SQLInstancesPort Fade2Black
This will display the instances and the port numbers on the server Fade2Black
.NOTES
AUTHOR: Rob Sewell sqldbawithabeard.com
DATE: 22/04/2015
#>
function Get-SQLInstancesPort
{
param ([string]$Server)
[system.reflection.assembly]::LoadWithPartialName("Microsoft.SqlServer.Smo")|Out-Null
[system.reflection.assembly]::LoadWithPartialName("Microsoft.SqlServer.SqlWmiManagement")|Out-Null
$mc = new-object Microsoft.SqlServer.Management.Smo.Wmi.ManagedComputer $Server
$Instances = $mc.ServerInstances
foreach($Instance in $Instances)
{
$port = @{Name ="Port"; Expression = {$_.ServerProtocols['Tcp'].IPAddresses['IPAll'].IPAddressProperties['TcpPort'].Value}}
$Parent = @{Name = "Parent"; Expression ={$_.Parent.Name}}
$Instance|Select $Parent,Name, $Port
}
}