I want to add an additional monitor to my new all-in-one. What would be the best cable to use?
The HDMI port on the back is for connecting an external monitor that has a HDMI input. You need a hdmi cable.
2.HDMI-out port Connect a TV or another HDMI-in enabled device. Provides video and audio output.*
*From the Manual-- https://topics-cdn.dell.com/pdf/inspiron-24-3477-aio_setup-guide_en-us.pdf