Retrieve All Wsp from the Central Admin

Add-PSSnapin Microsoft.SharePoint.PowerShell –erroraction SilentlyContinue
## setup our output directory 
$dirName = "c:\ExportedSolutions"
Write-Host Exporting solutions to $dirName 
foreach ($solution in Get-SPSolution) 
{ 
    $id = $Solution.SolutionID 
    $title = $Solution.Name 
    $filename = $Solution.SolutionFile.Name
    Write-Host "Exporting ‘$title’ to …\$filename" -nonewline 
    try { 
        $solution.SolutionFile.SaveAs("$dirName\$filename") 
        Write-Host " – done" -foreground green 
    } 
    catch 
    { 
        Write-Host " – error : $_" -foreground red 
    } 
}