When you set out to use Samsung DeX, it's easy to assume any USB-C cable will do — just plug the phone into a monitor and go. But when no image shows up, or it shows up cropped, the problem often isn't the DeX setting: it's the cable or adapter you picked. USB-C cables can look identical and behave very differently. Some are built only for charging or data transfer and simply can't send video to an external screen.
What to check before you buy
To plug the phone straight into a monitor or TV with a USB-C cable, the cable has to support video output — usually described on the box as DisplayPort Alt Mode. That's what lets the Galaxy push an image to an external screen, which is exactly what DeX needs to run over a cable in the first place.
For hubs and adapters, look for a model with a dedicated USB-C Power Delivery (PD) input. That lets you plug a charger into the hub and keep enough power flowing while DeX is running — without it, some accessories just won't hold the connection. It's also worth checking that the hub has the outputs you actually need (HDMI, USB ports for a keyboard and mouse) and that it supports the resolution you're aiming for.
What to avoid
Plain USB-C cables — especially the ones sold as "charging only" — often have no video support at all, even when they look identical to the ones that work. It's also worth avoiding hubs with no external power input: the spare power drawn from the phone itself tends to be limited, and that can undermine the stability of the connection while DeX is running — the same issue that shows up among the most common connection failures.
If the hub you already own does have a PD input, a charger with power to spare fixes a lot of these cases.
Check compatibility before you buy
Checking these specs before you buy avoids compatibility headaches and makes for a steadier connection while you're using DeX. If your Galaxy hasn't been confirmed yet, it's worth checking the list of supported models before spending on an accessory. And once you've got the right cable in hand, if the connection still won't work, the DeX troubleshooting guide gathers the most common causes and what to do about each. This note is part of the Samsung DeX complete guide.
The charger I use — Ugreen 100W charger (GaN, plenty of power to feed the hub and the phone at the same time).