The DC barrel jack input uses a switching power supply, allowing a wide input voltage range and is capable of powering a USB device connected to the USB host port that consumes 500mA (the legal maximum for USB).
Any supply between 7V and 15V is fine, the current it needs to deliver depends on what you plug into the USB host port. Rough ballpark figures: at 7V, 700mA is fine, at 15V, 250mA is enough. Center pin positive.
DC-plug center diameter should be 2.1 mm.
(there is also a 2.5mm plug variant, will fit too but maybe bad contact, not recommended)
5V on the DC barrel input is not enough. The editor will show you the actual voltage from the switching power supply. That should not be less than 4.75V.
You can also connect a USB cellphone/tablet-style charger to the micro-usb connector.