f1.txt
f2
f3.jpg

-- begin exclusions.txt --
a.txt
b.txt
c.txt
-- end --

# read all exclusions into a string array
$exclusions = Get-Content .exclusions.txt

dir -rec *.* | Where-Object {
   $exclusions -notcontains $_.name } | `
   Remove-Item -WhatIf

Get-ChildItem -exclude (gc exclusions.txt) | Remove-Item -whatif

$exclusions = Get-Content .exclusions.txt

dir -rec | where-object {-not($exclusions -contains [io.path]::GetFileName($_))} | `
where-object {-not($_ -is [system.IO.directoryInfo])} | remove-item -whatif