Both are dongles, $46 against $50. 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 TC35AL reaches 100 dB on 564 of the 567 models here, the Hidizs SD2 on 556.
| Specification | ddHiFi TC35AL | Hidizs SD2 |
|---|---|---|
| Power into 32Ω | 210 mW | 70 mW |
| Power into 150Ω | 45 mW | 15 mW |
| Power into 300Ω | 22 mW | 7.5 mW |
| Power into 600Ω | 11 mW | 3.7 mW |
| Output impedance | not published | not published |
| Output noise | not published | not published |
| Price | $46 | $50 |
| Headphones it reaches 100 dB on out of 567 | 564 | 556 |
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.
8 headphones reach 100 dB on the ddHiFi TC35AL but not on the Hidizs SD2 — HiFiMAN Susvara, Moondrop COSMO, Moondrop PARA 2, 5 more.
556 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 TC35AL and Hidizs SD2. Or put either against your own headphones in the source comparison tool.