Does USB Type C DisplayPort support automatically imply HDMI support?

Question

I recently bought a HP Envy 13 which has the following spec line for USB ports:-

• 2 USB 3.1 Type-C™ Gen 1 (Data Transfer up to 5 Gb/s, DP1.2, HP Sleep and Charge); 2 USB 3.1 Gen 1 (1 HP Sleep and Charge); 1 headphone/microphone combo

DisplayPort 1.2 support sounded promising. It's not thunderbolt, but at least I'd be able to use a dongle to connect external monitors for desk use. This works fine for the Type-C to VGA case (cheap no brand adapter), but the Type-C to HDMI case doesn't work at all (nothing shows up on either laptop or monitor).

My query to HP support was answered with the following (bolded exactly as posted in the response):-

• I am afraid that this setup will not work as only the USB Thunderbolt port supports USB - HDMI port.

What difference is there between 'DP1.2' support and normal USB Type-C (older HP devices, for example, don't state such support and just say they have 'USB Type-C')? Is this false advertising (this link clearly states support for 2 external 4K displays), or is there some crippled version of DP1.2 which only supports VGA adapters but not HDMI?

Answer 1

After various conversations with the local HP support staff and a visit to their national headquarters, it seems the initial response to me on the HP forums was mistaken. DP1.2 does indicate support for display over USB Type-C. Specifically, using DisplayPort Alternate Mode. This worked with a compatible adapter they had, but not the cheaper one I'd purchased online (and which is going to get returned now).

I'm not accepting this answer as its not a complete answer, but posting it for the benefit of anyone finding this on google.