Both are desktop amplifiers, $529 against $499. 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?
On raw power they are level: each reaches 100 dB on 567 of the 567 non-electrostatic models here.
| Specification | SMSL SP400 | Topping A90 |
|---|---|---|
| Power into 32Ω | 3.0 W | 2.0 W |
| Power into 150Ω | 741 mW | 427 mW |
| Power into 300Ω | 440 mW | 213 mW |
| Power into 600Ω | 220 mW | 107 mW |
| Output impedance | <0.1 Ω | 0.1 Ω |
| Output noise | 1.9 µV | 0.2 µV |
| Price | $529 | $499 |
| Headphones it reaches 100 dB on out of 567 | 567 | 567 |
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.
On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.
4 headphones stay below the audible-hiss threshold on the Topping A90 but cross it on the SMSL SP400 (Shure SE846, Simgot EA500, Tanchjim EA FORCE, 1 more).
567 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: SMSL SP400 and Topping A90. Or put either against your own headphones in the source comparison tool.