The power from an HDMI port carries 5v while most laptop chargers provide is usually 18-20v, so it’s considerably underpowered. If you connect to the wrong port (like two laptops that both have HDMI-OUT ports), you can short-circuit those laptops. HDMI ports do not provide the same safety features that your charging cable has. This means that there’s no protection when your laptop battery is full of charge (which is a problem when an HDMI offers slow charging, so you plug it in and walk away). Know that you only charge via HDMI temporarily. Sustaining the low-power charge can damage your laptop.
Only use this method if you’re sure that you have an HDMI-IN port as using an HDMI-OUT port may cause damage to both devices.
This method requires the use of an extra tool since many modern laptops have USB-C ports instead of HDMI-IN ports. If you don’t have an HDMI-IN port on your laptop, this adapter is required. You can purchase an HDMI-IN to USB-C Adapter from any electronics retailer. Make sure it’s an HDMI-IN to USB-C adapter since HDMI-OUT adapters are much more common.
This method requires the use of a universal adapter. With that device, you can even get charging tips if they are available for your make and model of laptop, so charging via HDMI is easy. You can purchase a universal adapter from any electronics retailer.
