Short answer
Both are desktop amplifiers, $100 against $109.
The Schiit Magni+ reaches 100 dB on 567 of the 567 models here, the Fosi Audio SK02 on 564.
| Specification | Fosi Audio SK02 | Schiit Magni+ |
|---|---|---|
| Power into 32Ω | 190 mW | 2.0 W |
| Power into 150Ω | 41 mW | 560 mW |
| Power into 300Ω | 20 mW | 260 mW |
| Power into 600Ω | 10 mW | 130 mW |
| Output impedance | not published | 0.2 Ω unverified |
| Output noise | 3.7 µV | 1.5 µV unverified |
| Price | $100 | $109 |
| Headphones it reaches 100 dB on out of 567 | 564 | 567 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Fosi Audio SK02 | Schiit Magni+ |
|---|---|---|
| Socket | 4.4mm | no separate rating |
| Power into 32Ω | 755 mW | — |
| Power into 300Ω | 80 mW derived | — |
| Output impedance | not published | — |
| Output noise | not published | — |
| Headphones it reaches 100 dB on out of 567 | 566 | — |
Only the Fosi Audio SK02 has a separate balanced rating from its maker; through it, it reaches 100 dB on 566 of the 567 models here. The Schiit Magni+ may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it. Derived figures are worked out from the loads the maker did publish.
| Load | Fosi Audio SK02 | Schiit Magni+ |
|---|---|---|
| 32 Ω | Published | Unverified |
| 150 Ω | Derived | Unverified |
| 300 Ω | Derived | Unverified |
| 600 Ω | Derived | Unverified |
Schiit Magni+ 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.
The Fosi Audio SK02 column does stand on a power rating its maker printed, at one of these four loads at least. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.
3 headphones reach 100 dB on the Schiit Magni+ but not on the Fosi Audio SK02 — Moondrop PARA, Symphonium Crimson, Symphonium Titan.
564 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 Beyerdynamic DT 1990 Pro (250Ω): Schiit Magni+ has +27 dB of headroom there against +16 dB. 11 dB is about 13 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Schiit Magni+ because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | Fosi Audio SK02 headroom | Schiit Magni+ headroom | Fosi Audio SK02 hiss | Schiit Magni+ hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +31 dB | +42 dB | 26 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +11 dB | +22 dB | 6 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +20 dB | +31 dB | 4 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +27 dB | -1 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +13 dB | +23 dB | -2 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +9 dB | +20 dB | -7 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB | +16 dB | -12 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +3 dB | +14 dB | -13 dB | not published |
The Schiit Magni+ costs $9 more than the Fosi Audio SK02. Out of the 567 models here, that difference buys 3 more models driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
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 Schiit Magni+ has published no electrical specification at all and everything above comes from independent measurement: Fosi Audio SK02 and Schiit Magni+.