The barrel power jack for the LTC2984 Dev Kit (Digi Key P/N DC2420A-KIT-ND) is a 2.1 mm ID x 5.5 mm OD center positive. per the manufacturer data sheet the specifications for an input are as follows.
AC ADAPTOR IN – 2.1mm × 5.5mm barrel connector.Optional DC power input, 7V to 20V DC. With external
power applied, up to 750mA can be drawn from the 5Vsupply (available on pins 2 and 5 on J3, or pin 10 on J1.) Here is a list of Power Supplies that meets those specifications.
For further information take a look at the LTC2984 Another Geek Moment Video