Download All Wsp solution from  Central Administration in SharePoint

 From the below script, You need to change the $dirName only .

 Run  The script in poweshell editor. or management shell.

$dirName = "<directory path>" 
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  
    }  
}

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