gci -Recurse -Filter *.zip |ForEach-Object {$n=($_.Fullname.trimend('.zip')); Expand-Archive -Path $_.Fullname -DestinationPath $n -Force}

Extract zip files to different location with same name (extracted folder name will contains .zip)

gci -Filter *.zip |ForEach-Object {Expand-Archive -Path $_ -DestinationPath C:\Temp\$_ -Force}

Extract zip files to different folder location, this will extract the zip files including sub folders in destination)

PS C:\Temp\tt> gci -Recurse -Filter *.zip |ForEach-Object {$n=($_.Fullname.trim('C:\Temp .zip')); Expand-Archive -Path $_.Fullname -DestinationPath C:\TempT\$n -Force}

Get-ChildItem 'path to folder' -Filter *.zip | Expand-Archive -DestinationPath 'path to extract' -Force

Also, this one it is a bit complex but it works

PARAM (
     $ZipFilesPath = "X:\Somepath\Full\Of\Zipfiles",
     $UnzipPath = "X:\Somepath\to\extract\to"
)
 
$Shell = New-Object -com Shell.Application
$Location = $Shell.NameSpace($UnzipPath)
 
$ZipFiles = Get-Childitem $ZipFilesPath -Recurse -Include *.ZIP
 
$progress = 1
foreach ($ZipFile in $ZipFiles) {
    Write-Progress -Activity "Unzipping to $($UnzipPath)" -PercentComplete (($progress / ($ZipFiles.Count + 1)) * 100) -CurrentOperation $ZipFile.FullName -Status "File $($Progress) of $($ZipFiles.Count)"
    $ZipFolder = $Shell.NameSpace($ZipFile.fullname)
 
 
    $Location.Copyhere($ZipFolder.items(), 1040) # 1040 - No msgboxes to the user - http://msdn.microsoft.com/en-us/library/bb787866%28VS.85%29.aspx
    $progress++
}

I want to unzip all zip-files in this folder to "\\zipped\Unzipped" folder.

It seems expand-archive cmdlet only support one file at a time.
So do you need to create an array with all filenames and then create a loop to unzip all files?