I have the 17" model and I'm trying to buy a dock device that will allow me to run 2 external monitors, but they require the USB 3.1 Gen 1 ports to have DisplayPort Alt Mode. All the specs I can find so far don't say they are data only, but they don't say they can do video either. Does anybody know or know where to find a definitive answer on that?
Looking at the port information in the system’s Setup and Specifications document (https://topics-cdn.dell.com/pdf/inspiron-17-3780-laptop_users-guide_en-us.pdf), there’s no indication of a USB-C port at all. That’s the US version document though, and I’ve seen at least one case where another region’s version of a system included a Type-C port when the US version didn’t.
In any case, do you have the DIsplayPort “DP” logo printed next to your Type-C port? If so, then you have DP Alt Mode. If not, then you still might, but it’s not a guarantee.
@Marty_L I just realized you were asking about the 3.1 Gen 1 ports. DP Alt Mode is only available from USB-C ports. It is never available from regular USB-A ports. If you were planning to get a USB-C dock that relied on DP Alt Mode for video (which is most of them) and connect it your system using a female USB-C to male USB-A adapter, that will never work. Your only way to use multiple displays from a USB-A port is with a dock that relies on DisplayLink technology, such as the Dell D6000, but DisplayLink has some drawbacks that can be serious for certain use cases. Check the post I wrote that’s marked as the answer in this thread:
@jphughan Thank you for your reply! I did not know that only USB-C did the DP Alt Mode. But it sounds like this laptop can do video through the USB 3.1 port, just not the DP Alt Mode, is that correct?
@Marty_L that's sort of true. There's nothing inherent about that laptop's regular USB ports, or any regular USB ports anywhere, for that matter -- that allows them to carry video. However, it is true that by using certain combinations of appropriate software and USB peripherals, such as DisplayLink drivers and DisplayLink USB graphics adapters (or a DisplayLink-based dock), it is possible to send a video signal over USB. In that setup, the DisplayLink drivers convert the video signal to regular old USB data prior to sending it over USB, and then the DisplayLink chip inside the adapter/dock converts that back to regular video prior to sending it to displays. So the USB ports themselves don't need any special capabilities in this scenario, because they're only ever carrying regular old USB data. It's the components on either end of the link that are doing all the work.