Export-SPSolution.ps1

function Export-All-XSPSolution ($Location)
{
    $farm = Get-SPFarm
    If (test-path $Location) {} Else {mkdir $Location}
    Write-Host "Downloading..."
 
    $farm.Solutions

    foreach($solution in $farm.Solutions){   
        $solution = $farm.Solutions[$solution.Name]
        $file = $solution.SolutionFile
        $file.SaveAs($Location + ‘\’ + $solution.Name)
    }
 
    Write-Host "All the solutions are downloaded to $Location"
}

$timestamp = Get-Date -format "yyyyMMddHHmmss"
$path = "D:\BackupWsp\$timestamp"

Export-All-XSPSolution -Location $path