Quick answer
For advanced users: Check your USB-C cable supports DisplayPort Alt Mode (not just power), then unplug all other USB-C devices, and restart your Mac while the monitor is connected. That clears the handshake issue 80% of the time.
Why this happens
The U2720Q is a great monitor, but it's picky about the USB-C cable and your Mac's port negotiation. The error "No signal via USB-C" usually means the monitor isn't receiving a valid DisplayPort signal over the USB-C connection. This can happen because the cable you're using is charge-only, or because macOS decides your MacBook Pro is a secondary display and sends no signal to the monitor. I've seen this trip up people who just unpacked a new MacBook Pro—they assume any USB-C cable works. It doesn't.
Another common trigger: you've got a USB-C hub or another display connected, and macOS gets confused about which port to use. The U2720Q is also notorious for needing a firmware update if you're running macOS Big Sur or later—the older firmware just doesn't negotiate properly with Apple Silicon or even some Intel Macs.
Fix steps
- Swap the cable. Use the USB-C cable that came with the U2720Q. If you lost it, buy one that explicitly states "DisplayPort Alt Mode" or "4K 60Hz USB-C cable." Avoid cheap cables that only support USB 2.0 data and power. This is the #1 fix.
- Plug into the right port. On the U2720Q, use the USB-C port labeled with a DisplayPort icon (usually the one on the back, next to the DP inputs). The other USB-C port might be for data only.
- Power cycle everything. Unplug the monitor's power cable, unplug the USB-C from your Mac, wait 10 seconds, plug the monitor back in, and then connect the USB-C. This resets the monitor's EDID handshake.
- Restart your Mac with the monitor connected. Keep the USB-C plugged in, then restart your MacBook Pro. Even if the screen is black, let it boot—macOS often re-detects the display after a restart.
- Check display settings on your Mac. Go to
System Settings > Displaysand look for the U2720Q. If it's not there, hold the Option key and click "Detect Displays"—it forces a rescan.
If that doesn't work
Update the monitor firmware
Head to Dell's support page for the U2720Q and grab the latest firmware. It's a Windows-only utility, so you'll need a PC or use a friend's—or run a Windows VM with USB passthrough. I know that's annoying, but the firmware update fixes the Mac-specific handshake bugs. Version M2B102 or later works well with macOS Ventura.
Reset the monitor's settings
On the monitor's OSD, go to Others > Factory Reset. This clears any weird display settings that might be blocking signal.
Try a different Mac port
Some MacBook Pro models have a flaky port for external displays. If you're using a left-side port, try the right side. Also avoid using a USB-C hub—connect directly to your Mac.
Check your macOS display scaling
If the monitor is detected but shows black, it might be a scaling issue. In System Settings > Displays, switch to "Default for display" instead of scaled.
Prevention tip
Always keep a dedicated USB-C cable for the monitor. Don't borrow the one from your phone charger—it might not support DisplayPort. And when you update macOS, plug the monitor in before you update, then restart after. That way the display handshake is refreshed. I've had clients avoid this entire headache by labeling the cable that came with the monitor.