Dell WD22TB4 Thunderbolt Dock on a MacBook Air: Measured
The Dell WD22TB4 Thunderbolt dock on a MacBook Air M5: a 90 W contract at 4.5 A, Thunderbolt 4 at 40 Gbps, and gigabit ethernet, all over one cable.
The Dell WD22TB4 Thunderbolt dock, tested against a MacBook Air M5 with a low battery, per the methodology. Unlike every charger in this series, a dock’s power contract is only part of what the cable is carrying.
The numbers
| Charging rated | 90 W |
| Negotiated | 90 W (20 V up to 4.5 A) |
| Live draw | 60.7 W (20 V at 3.49 A) |
| Protocol | USB PD 3.0 |
| Link speeds | 40 Gbps, 10 Gbps, 5 Gbps, 480 Mbps |
| Versions | Thunderbolt 4, USB 3.1, USB 2.1 |
Profile menu:
| Profile | Rail |
|---|---|
| 15 W | 5 V up to 3 A |
| 27 W | 9 V up to 3 A |
| 45 W | 15 V up to 3 A |
| 90 W | 20 V up to 4.5 A |
| 130 W | 20 V up to 6.5 A (Dell proprietary) |
The 6.5 Amp Dell proprietary profile
While the Mac negotiates a standard 90 W (20 V at 4.5 A) Power Delivery contract, this dock also broadcasts a proprietary 130 W profile (20 V at 6.5 A) meant exclusively for compatible Dell laptops.
Standard USB-C Power Delivery limits current to 5 amps. Dell bends the USB-C specification by pushing 6.5 amps through the connector, which requires both their own laptops and their own docks to safely negotiate. Because a MacBook is a standard USB-C device, it safely ignores the proprietary extension and falls back to the standard 4.5 A profile instead.
The 4.5 A top standard rung
The top standard profile draws 4.5 A, which is past the 3 A ceiling of a USB-C cable without an e-marker chip. Reaching the full 90 W therefore requires a 5 A e-marked cable - on a plain one you would negotiate 60 W and see no explanation for the shortfall.
Most Thunderbolt docks ship with a suitable captive or bundled cable, but it is worth knowing that the dock’s headline wattage assumes it.
What makes a dock different
A charger negotiates power. A dock negotiates power and everything else, simultaneously, over the same connector:
- Thunderbolt 4 at 40 Gbps for displays and storage
- USB 3.1 and USB 2.1 device tunnels
- A Realtek gigabit LAN adapter, enumerating as its own USB device at 5 Gbps
- 90 W of charging
The ethernet adapter is the clearest illustration. It shows up in the app as a separate connected device with its own speed, version, and vendor - a whole network interface riding the same cable that is delivering 90 W to the battery.
That is the actual argument for a dock over a charger: not more power, but power arriving on a cable that is also doing four other jobs at once. See Thunderbolt 4 vs. USB4 for how these link types differ.