PowerConnect 5500 series switches use two HDMI 10G ports for stacking.
https://www.dell.com/support/article/zh-hk/how10728/how-to-stack-dell-networking-powerconnect-5500-model-switches?lang=en
https://www.dell.com/support/article/zh-hk/how10728/how-to-stack-dell-networking-powerconnect-5500-model-switches?lang=en