Here's the PowerShell equivalent:
```
$dir1 = 'C:\path\to\dir1'
$dir2 = 'C:\path\to\dir2'
$cmd1 = 'your Powershell command here {} {}'

Get-ChildItem -Path $dir1 -Recurse | Where-Object { $_.Extension -eq '.csv' } | ForEach-Object {
    $file1 = $_.FullName
    $file2 = Join-Path -Path $dir2 -ChildPath $file1.Substring($dir1.Length)
    & $cmd1 -f $file1, $file2
}
```
Explanation:

Get-ChildItem -Path $dir1 -Recurse recursively lists all files and directories in dir1
Where-Object { $_.Extension -eq '.csv' } filters the list to only .csv files
ForEach-Object loops over the filtered list
$_ represents each .csv file
$_.FullName gets the full path of the current .csv file
Join-Path constructs the path in dir2
$file1.Substring($dir1.Length) gets the relative path of the file in dir1
& invokes a subprocess to run the command $cmd1 with the file paths as arguments
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