Short answer
Both are dongles, both at $9.
The Apple USB-C dongle (US) reaches 100 dB on 547 of the 567 models here, the Apple USB-C dongle (EU) on 516.
| Specification | Apple USB-C dongle (EU) | Apple USB-C dongle (US) |
|---|---|---|
| Power into 32Ω | 15 mW | 30 mW |
| Power into 150Ω | 4.0 mW | 8.0 mW |
| Power into 300Ω | 2.0 mW | 4.0 mW |
| Power into 600Ω | 1.0 mW | 2.0 mW |
| Output impedance | 1 Ω unverified | 1 Ω unverified |
| Output noise | 6 µV unverified | 6 µV unverified |
| Price | $9 | $9 |
| Headphones it reaches 100 dB on out of 567 | 516 | 547 |
| Load | Apple USB-C dongle (EU) | Apple USB-C dongle (US) |
|---|---|---|
| 32 Ω | Unverified | Unverified |
| 150 Ω | Unverified | Unverified |
| 300 Ω | Unverified | Unverified |
| 600 Ω | Unverified | Unverified |
Neither of these two makers publishes no electrical specification at all. That is true of 10 of the 280 sources here, and the figures in that column come from independent measurement rather than from a maker document — which is not worse, but it is not the same thing, and it cannot be checked against anything the maker will stand behind.
31 headphones reach 100 dB on the Apple USB-C dongle (US) but not on the Apple USB-C dongle (EU) — AKG K612 Pro, Abyss AB-1266 Phi CC, Abyss AB-1266 Phi TC, 28 more.
516 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Campfire Audio Andromeda 2020: Apple USB-C dongle (US) has +3 dB of headroom there against +0 dB. 3 dB is twice the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Apple USB-C dongle (EU) and Apple USB-C dongle (US) because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Apple USB-C dongle (EU) headroom | Apple USB-C dongle (US) headroom | Apple USB-C dongle (EU) hiss | Apple USB-C dongle (US) hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +20 dB | +23 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +0 dB | +3 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +10 dB | +13 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +6 dB | +9 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +2 dB | +5 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | -1 dB | +2 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | -5 dB | -2 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -8 dB | -5 dB | not published | not published |
These two cost the same, $9, so price settles nothing. Out of the 567 models here, the Apple USB-C dongle (US) drives 31 models to 100 dB — and on the other side there is no such advantage at all.
Only published figures count here; blank axes are counted separately.
Each has a page of its own with a full headphone list and the provenance of every figure — worth opening here, because Apple USB-C dongle (EU) and Apple USB-C dongle (US) have published no electrical specification at all and everything above comes from independent measurement: Apple USB-C dongle (EU) and Apple USB-C dongle (US).