There isn't currently a built-in PowerShell method for doing the SFTP part. You'll have to use something like psftp.exe or a PowerShell module like Posh-SSH.
Here is an example using Posh-SSH:
# Set the credentials
$Password = ConvertTo-SecureString 'Password1' -AsPlainText -Force
$Credential = New-Object System.Management.Automation.PSCredential ('root', $Password)
# Set local file path, SFTP path, and the backup location path which I assume is an SMB path
$FilePath = "C:\FileDump\test.txt"
$SftpPath = '/Outbox'
$SmbPath = '\\filer01\Backup'
# Set the IP of the SFTP server
$SftpIp = '10.209.26.105'
# Load the Posh-SSH module
Import-Module C:\Temp\Posh-SSH
# Establish the SFTP connection
$ThisSession = New-SFTPSession -ComputerName $SftpIp -Credential $Credential
# Upload the file to the SFTP path
Set-SFTPFile -SessionId ($ThisSession).SessionId -LocalFile $FilePath -RemotePath $SftpPath
#Disconnect all SFTP Sessions
Get-SFTPSession | % { Remove-SFTPSession -SessionId ($_.SessionId) }
# Copy the file to the SMB location
Copy-Item -Path $FilePath -Destination $SmbPath
Some additional notes:
That should give you a decent starting point.