This message was posted on behalf of Intel Corporation
Thank you for joining the Intel® NUC Community. I am sorry to hear you are having power issues with the Intel® NUC.
Based on the specification for the DC Input Voltage Supported for this model, it states that the board can be powered through a 12-19 V DC connector on the back panel. So, there shouldn't be any issues while using this voltage, it must have been a faulty unit. I checked the ticket number you generated and noticed that there is warranty process going on for the unit, so I hope you get the replacement unit as soon as possible. In case you have more questions regarding this process, please refer to that case number.
You can check the DC Input Voltage Supported specification here: https://www.intel.com/content/dam/support/us/en/documents/boardsandkits/NUC7i3BN_TechProdSpec.pdf