Fiio just released amazing 160$ upgrade for all of their devices - Darkside Pro review

https://www.youtube.com/watch?v=FWeBx_hvXoA

There's a particular kind of audiophile frustration that nobody talks about loudly enough. You've spent real money on a DAC. You've agonized over its chip architecture, its output stage topology, its measurements. You've read every review. You bought it. It sounds good. Maybe even great. But there's something slightly veiled about it, something that doesn't quite let go, a faint hardness in the upper midrange that you keep telling yourself you'll get used to. You don't get used to it. You start looking at cables.

Stop. Before you spend money on cables, look at what's powering the thing.

That's the argument FiiO is making with the Darkside Pro, and it's a more interesting argument than the product's modest appearance might suggest. At $159.99, this is a linear power supply — not a DAC, not an amplifier, not anything that actually touches the signal. It just feeds electricity to your gear. Quietly. Cleanly. Without drama. And whether or not you believe power supplies audibly matter (we'll get to that), the Darkside Pro forces a conversation that the hi-fi industry tends to paper over: the gear we love often arrives powered by components chosen for cost rather than quality.

The Lie of the Bundled Wall Wart

Let me be direct about something. A lot of entry-level and mid-tier audio gear — from FiiO, Topping, SMSL, WiiM, Eversolo — ships with pretty mediocre power supplies. Cheap switching adapters. Lightweight wall warts that technically get the job done but do not exactly help performance.

This is industry-wide and largely unspoken. A DAC manufacturer invests heavily in its signal path — the input receiver, the DAC chip, the output stage — and then routes power from a $4 switching adapter into all of it. The adapter is chosen because it's cheap, small, and passes regulatory testing. Nobody puts it in the product spec sheet. Nobody highlights it in the marketing. It just ships in the box, coiled beside the USB cable, and most buyers never think about it again.

The Darkside Pro is FiiO essentially admitting that this matters. That's not a small thing for a brand to do publicly.

What the Darkside Pro Actually Is

The Darkside Pro is intended as a universal external power supply for hi-fi components that rely on DC input. Typical applications include network players, digital-to-analog converters, compact preamplifiers, and desktop headphone amplifiers.

It is compact enough to sit neatly in a desktop system. At the same time, it feels dense enough to suggest a proper transformer-based design rather than a dressed-up utility box. It weighs around 2,200 grams — exactly the kind of heft one hopes to find in a linear supply. FiiO makes the chassis from heavy-duty unibody aluminium alloy and offers it in black or silver. At 188 by 188 by 42.3 millimetres, it keeps a neat footprint and a restrained appearance.

That footprint is significant. One of the ongoing criticisms of linear power supplies as a category is that they're large, heavy, and run warm — tolerable in a dedicated listening room, less so on a cluttered desk. FiiO has clearly engineered around this constraint. The Darkside Pro is flat, almost like a book lying face-down, and slides under most components without demanding its own shelf.

At its core is a toroidal transformer designed specifically for low-noise audio, utilizing a grain-oriented silicon steel circular core process for higher efficiency and minimized eddy currents. The seamless, fold-free coil design ensures a uniform magnetic field and minimal magnetic leakage.

Dual high-current IRFZ34NPBF MOSFETs are used in a parallel configuration to lower internal resistance. That parallel configuration is important — it's not just about raw current capacity, but about keeping the output impedance low so the supply can respond instantly when connected digital components demand sudden current during dynamic passages.

A rear-panel switch lets you select the output voltage, while a precision potentiometer allows fine adjustment within ±0.2 volts. This fine-tuning capability is something I appreciate beyond its obvious utility. It signals engineering confidence — they're not just handing you a nominal voltage and hoping your device doesn't care.

Switching vs. Linear: The Physics of Clean Power

Before making any sonic claims, it's worth being honest about what the engineering actually does — and what it doesn't.

A switching power supply (SMPS) works by chopping the incoming AC current at high frequency, typically tens to hundreds of kilohertz, and using that pulsed signal to drive a small transformer. The efficiency is excellent — most of the energy ends up as useful DC output rather than heat. That's why switching supplies are compact and run cool. The problem is the chopping itself. That switching frequency creates electromagnetic interference that ripples through the output voltage and, through the ground planes and supply rails of your audio components, can measurably increase the noise floor of everything downstream.

A linear power supply takes the opposite approach. It uses a large transformer to step down the mains voltage directly at 50 or 60Hz, rectifies it, and then smooths and regulates the resulting DC with a series of filtering stages. No high-frequency switching. No switching noise. Instead of switching at high frequencies, it focuses on delivering a smooth, stable DC voltage with minimal ripple and interference.

The trade-offs are real and shouldn't be ignored. Linear supplies are heavier, larger, and run warmer. They're less efficient — some energy becomes heat in the regulation stage. And a poorly designed linear supply can still introduce noise; the topology is necessary but not sufficient. That alone doesn't guarantee quality, since poorly designed linear supplies can still introduce noise and other issues.

What the Darkside Pro's integrated relay does is manage the transformer's output voltage to provide a precise match for both the 12V and 15V settings, maximizing power efficiency and significantly reducing heat generation during operation. This relay-switched approach to voltage selection is more precise than a simple tap-change on the transformer — it keeps the operating point of the regulation stage consistent regardless of which voltage you've selected.

Here's the lateral thinking point that reviews often skip past: the audible benefit of a linear supply isn't that it "sounds better" in some mystical sense. It's that it removes a source of contamination that was masking the true performance of your component. Think of it less like an upgrade and more like cleaning a dirty lens. The image doesn't change — the obstruction goes away.

Compatible Devices: The FiiO Ecosystem and Beyond

Compatible FiiO devices include the K11, K11 R2R, K13 R2R, K15, K19, R9, R7, TT13, K5 Pro series, K7 series, Q7, and all FiiO portable players using Type-C power supply. Bloom Audio

That list deserves a closer look, because some of these pairings make considerably more sense than others.

The K13 R2R is the obvious flagship pairing. R2R DAC architectures — those using resistor ladder networks instead of modern delta-sigma chips — are categorically more sensitive to power supply noise. The resistor network operates in the analog domain and generates its output voltage directly from the supply rail. Any noise on that rail becomes noise in the signal. R2R designs can be sensitive to supply noise and small voltage variations. Rather than "adding a new sound," a cleaner supply can help the system feel more controlled: quieter backgrounds, smoother transitions, and more coherent timing. This is where I'd expect the Darkside Pro to earn its money most convincingly.

The R7 streaming DAC is another strong candidate. Network streamers contain switching circuitry, Wi-Fi radios, embedded processors — a mess of noise-generating digital infrastructure living in the same box as the analog output stage. A cleaner external supply doesn't eliminate that internal noise, but it removes one vector for contamination.

Beyond FiiO's own line, the Darkside Pro is also compatible with third-party DACs, streamers, and headphone amps that rely on external DC power. The 12V/15V switchable output covers the majority of the desktop audiophile ecosystem. WiiM streamers, SMSL DACs, Topping headphone amplifiers — if it runs on 12V DC and uses a standard barrel connector, the Darkside Pro can likely power it.

One limitation worth naming: this is a single-output unit. It cannot simultaneously power two devices — which is a real constraint for setups like a K13 paired with a USB CD drive. FiiO could have addressed this with dual outputs; they didn't. For systems with multiple DC-powered components, you'd need multiple units, which starts to feel philosophically inelegant.

The Competitive Landscape

The audiophile linear power supply market is more crowded than most people realize, and FiiO is entering it at an interesting price point.

The most discussed competitors are the iFi iPower Elite, the Farad Super3, the Sbooster, and further up the pricing ladder, units from Paul Hynes, JCAT, and UpTone Audio.

The iFi iPower Elite deserves an honest clarification: all iFi iPower models, including the Elite, are SMPS units — switching supplies with active noise cancellation, not true linear designs. They measure extremely well and are more compact than any linear alternative, but they are not the same category of device as the Darkside Pro. Comparing them is legitimate, but they solve the noise problem differently.

The Farad Super3 is the most credible true linear competitor in terms of reputation. It uses supercapacitors as part of its energy storage, claiming sub-1µV noise floor figures, and it occupies roughly the same price territory — perhaps slightly above the Darkside Pro depending on configuration. The Farad Super3 is a great value, especially if you enjoy a more liquid and smooth sound. The Super3 has a strong following among Chord DAC users in particular.

The Sbooster offers a similar linear topology with a brand-specific "Ultra" upgrade path and is widely used among WiiM and Naim streamer owners.

Where the Darkside Pro differentiates itself is in explicit ecosystem integration. FiiO has engineered this supply with its own product line in mind — the GX16-2 aviation connector, the voltage selection range, the 3A current headroom — and that thoughtfulness shows. You're not adapting a generic linear supply to work with FiiO gear; you're using a supply that FiiO designed around its gear. That specificity has real value even if it narrows the product's identity somewhat.

For Whom Is This?

Let me try to be precise rather than diplomatic, because "for audiophiles who want cleaner power" is not a useful answer.

The Darkside Pro makes strongest sense for: owners of the FiiO K13 R2R or K11 R2R whose systems are otherwise well-resolved — good speakers or headphones, decent amplification — and who feel the DAC is capable of more than it's currently delivering. R2R topologies are the most supply-sensitive architecture in consumer hi-fi; the potential gain here is real and measurable, not just subjective.

It makes very good sense for: R7 and K7 owners who are using them in resolved desktop systems and are experiencing any form of graininess or compressed dynamic feel that doesn't track with what reviews suggest the unit should do.

It makes reasonable but more modest sense for: modern delta-sigma DAC users. ESS and AK chips have substantial internal regulation and noise rejection built into the chip architecture. They benefit from clean power, but the returns are less dramatic. You'd hear the difference in A/B testing; whether you'd pay $159 for it in isolation is a personal calculus.

It makes limited sense for: anyone whose current system bottleneck is clearly elsewhere — the speakers, the room, the amplifier's own power supply.

A linear external supply cannot fix an underpowered integrated amplifier or a room with no acoustic treatment.

The uncomfortable honest truth about power supply upgrades is that they operate in the lower percentile of system gains. They are real, they are measurable, they can be audible — but you need to have addressed the higher-gain problems first or you simply won't hear the improvement clearly enough to evaluate it.

Conclusion

The FiiO Darkside Pro is a well-engineered product that answers a question the industry mostly refuses to ask out loud. If you've spent $300–$500 on a FiiO DAC or streamer, you've almost certainly been running it on a power supply worth a tenth of that. The Darkside Pro corrects that imbalance.

The real question is not simply whether it works. It is how convincingly it makes its case. And for the specific pairing of the K13 R2R — which is the unit I'd pair this with without hesitation — I think the case is genuinely compelling. R2R DACs and noisy switching supplies are a bad marriage. This is a clean divorce.

At $159.99, it isn't cheap for what is essentially an accessory. But it's not expensive for what it actually is: a serious, transformer-based linear supply with discrete regulation, meaningful engineering behind it, and a voltage output range that covers most of the desktop audiophile ecosystem. The competitors — Farad, Sbooster, UpTone — are either similarly priced or considerably more expensive.

My only real criticism is the single output. A second output port, even at lower current, would have elevated this from a smart accessory to a genuinely essential desktop hub. That omission feels like a version 2 waiting to happen.

If you own FiiO R2R gear and your system is resolved enough to tell the difference — buy it. If you're still on your first desktop DAC paired with budget headphones, address those first. And if you're the kind of person who has been eyeing an aftermarket cable as your next upgrade, I'd strongly encourage you to look at this instead. Cables move energy around the room. The Darkside Pro cleans up what's already there.

Pros

Clean linear power supply design The Darkside Pro uses a proper transformer-based linear design, aiming to reduce switching noise, ripple, and electrical contamination compared with cheap bundled wall-wart adapters.

Strong match for FiiO R2R DACs It makes the most sense with devices like the FiiO K13 R2R and K11 R2R, where cleaner power can matter more because R2R designs are more sensitive to supply noise and voltage stability.

Solid build quality It its dense feel, heavy-duty unibody aluminium chassis, compact footprint, and substantial 2,200 g weight, giving it the feel of a serious audio accessory rather than a cheap utility box.

Compact for a linear power supply Unlike many bulky linear supplies, the Darkside Pro has a flat, desk-friendly form factor that can slide under other components without needing a dedicated shelf.

12V/15V compatibility The switchable voltage output makes it useful with many desktop DACs, streamers, headphone amps, and compact preamps, both inside and outside the FiiO ecosystem.

Fine voltage adjustment The precision potentiometer with ±0.2V adjustment adds useful control and suggests a more serious engineering approach than simply offering fixed nominal voltage.

Good value against high-end competitors At $159.99, it is positioned below or around many respected linear power supply competitors like Farad, Sbooster, UpTone, and Paul Hynes options.

Potentially more meaningful than cable upgrades I argue that, for some systems, improving power quality may be a more rational upgrade than spending money on aftermarket cables.

Cons

Single output only The biggest criticism is that it can power only one device at a time. For desktop systems with multiple DC-powered components, that becomes limiting.

Not a universal miracle upgrade It makes clear that this will not fix bigger system problems like poor speakers, bad room acoustics, or weak amplification.

Benefits depend heavily on the system The improvement is likely more obvious in resolved systems and with sensitive devices like R2R DACs. In more basic systems, the difference may be too subtle to justify the cost.

Less dramatic with modern delta-sigma DACs ESS and AKM-based DACs often have strong internal regulation and noise rejection, so the audible benefit may be smaller compared with R2R designs.

Still expensive as an accessory At $159.99, it is not cheap for something that does not decode, amplify, stream, or directly touch the signal path.

Linear power supply trade-offs remain Like most linear supplies, it is heavier, less efficient, and likely warmer-running than a compact switching adapter.