Backup-DhcpServer -path C:\DhcpBackupFolder
This command will create a sub-folder called NEW containing the database backup files and a file called DhcpCfg in the root of the target backup folder. You need both the config file and the files in the backup folder in order to restore.
If you should ever have to restore your DHCP server from your powershell-driven backup process, you will first need to copy the config file and "new" subdirectory contents to the "%SystemRoot\System32\DCHP\backup" folder before the DHCP restore operation will function properly.
If you would rather use Powershell instead of the GUI for the restore, the command is as follows:
Restore-DhcpServer -ComputerName "ServerNameHere" -path "C:\Windows\sytem32\dhcp\backup"