Comment by cesarb

> And it's the actual GPU that's outputting a HDMI signal over the Displayport connector, which the adapter than rewires in to a HDMI shaped connector.

There are two kinds of DP to HDMI adapters. The passive ones are like you said, they need special support on the GPU (these ports are usually labelled as DP++), IIRC they only do some voltage level shifting. The active ones work on any DP port (they don't need AFAIK any special support on the GPU), and they do the full protocol conversion.