I have a list of folks and their DN from AD (I do not have direct access to that AD). Their DNs are in format:
$DNList = \'CN=Bob Dylan,OU=Users,OU=Dept,OU=
Similar to Grahams answer but removed the hardcoded array values so it will just remove the CN portion without worrying how long the DN is.
$DNList | ForEach-Object{($_ -split "," | Select-Object -Skip 1) -join ","}
Ansgar most likely has a good reason but you can just use regex to remove every before the first comma
$DNList -replace "^.*?,"
Update based on briantist
To maintain a different answer but one that works this regex can still have issues but I doubt these characters will appear in a username
$DNList -replace "^.*?,(?=OU=)"
Regex uses a look ahead to be sure the , is followed by OU=
Similarly you could do this
($DNList | ForEach-Object{($_ -split "(,OU=)" | Select-Object -Skip 1) -join ""}) -replace "^,"