This FAQ explains which power connector is used in the following devices:

• ES-246/257/313/320/701/279
• BL-819 and BL-830

The power jack is a type 2 EIAJ RC-5320A Connector.
The socket has a:

• 1.65mm inner pin diameter
• 4.4mm socket internal diameter

It is designed to mate with a plug with a 4mm outer diameter.
The power supply for this socket can be bought from Brainboxes part number PW-800: