This will find duplicate files from one folder to another.

find-duplicates.ps1

[cmdletbinding()]
param(
    [string]$sourceFolder = $pwd
)

function Find-DuplicateFiles{
    [cmdletbinding()]
    param(
        [string]$sourceFolder = $pwd
    )
    process{
        $allFiles = ((Get-ChildItem -Path $sourceFolder -Recurse -File).FullName)

        [hashtable]$filehashmap = @{}

        foreach($file in $allFiles){
            if( ([string]::IsNullOrWhiteSpace($file)) -or (-not (test-path $file)) ){
                continue
            }

            $fhash = Get-FileHash -LiteralPath $file
            if(-not ($filehashmap.ContainsKey($fhash.Hash))){
                $filehashmap[$($fhash.Hash)] = @()
            }

            $filehashmap[$($fhash.Hash)] += $file
        }

        $filehashmap.Keys| %{
            $current = $_
            if($filehashmap[$current].Count -gt 1){
                # $filehashmap[$current]
                '-----' | Write-Output
                New-Object -TypeName psobject -Property @{
                    Hash = $current
                    Files = $filehashmap[$current]
                }
            }
        }
    }
}

Find-DuplicateFiles -sourceFolder $sourceFolder