Both are dongles, $46 against $60. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The ddHiFi TC35Air reaches 100 dB on 564 of the 567 models here, the Kiwi Ears Allegro Pro on 554.
| Specification | ddHiFi TC35Air | Kiwi Ears Allegro Pro |
|---|---|---|
| Power into 32Ω | 210 mW | 68 mW |
| Power into 150Ω | 45 mW | 15 mW |
| Power into 300Ω | 22 mW | 7.3 mW |
| Power into 600Ω | 11 mW | 3.6 mW |
| Output impedance | not published | not published |
| Output noise | not published | not published |
| Price | $46 | $60 |
| Headphones it reaches 100 dB on out of 567 | 564 | 554 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
10 headphones reach 100 dB on the ddHiFi TC35Air but not on the Kiwi Ears Allegro Pro — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 7 more.
554 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: ddHiFi TC35Air and Kiwi Ears Allegro Pro. Or put either against your own headphones in the source comparison tool.