Does it make any difference (quality-wise and input-delay-wise) if I use a DisplayPort to HDMI cable directly or a DisplayPort to HDMI adapter, followed by a regular HDMI cable?
Yes and no.
At the frequencies that HDMI operates, the path a signal takes can interfere with that signal. It’s why sometimes a cheap HDMI cable causes issues, where one certified for 4K or 8K doesn’t - the requirements to carry more information, means higher frequencies and thus better shielding.
A connector is a potential location where signal can be affected if the connection between two conductors is poor.
In general, less connectors and less joins will give you a higher chance of success and less chance of interference, but it depends entirely on what type of distance and signal you’re trying to send across it.
In general, the shorter the connection, the less loss.
It might be that a single longer cable is worse than a connector and a short cable.
If you already have a connector and a HDMI cable, try it. If you have issues, start by reversing the HDMI cable. It won’t make the electrons reverse or anything like that, but the connection might be slightly different.
If you have neither, I’d get a cable without a join. Buy from people who take returns.
Budget will be the determining factor for most people.
TL;DR; try it.
Edit: from the other answers, I’m probably wrong - maybe don’t trust this as correct
I don’t think so - HDMI and Display Port actually carry their signals in the same way, so the adapter is basically just converting between two plug types without any smarts in the middle.
In theory you could get an adapter that is badly made and adds some noise to the signal or something and forces the monitor to down-spec it’s signal but I’m not sure how likely that is to come across.
In my experience, in IT, cables are usually the way to go over adapters. Adapters tend to break more often than cables.
Someone else may offer a more thorough differing opinion… like perhaps a very high quality HDMI cable with a high quality adapter may be better than a mediocre off-brand standalone cable, but if the prices/brand are the same… I’d stick with the single cable.
Before USB-C became standard, we stuck with HDMI cables and then had different adapters on hand just for convenience, but if we knew a cable is going to be used in the same equipment for a long time, we’ll try for the single cable.
My adapter and most I found could not do 120Hz at 4K, but the cables were easier and cheaper to buy.
