USB-C’s lingering incompatibilities and complexities, part 2: Splitter issues

Yours truly can’t try to do the splits without ending up in the hospital, and suspects many of you would find the maneuver equally complicated-to-impossible…as does, it turns out, USB.

In last week’s initial post of this series, I discussed ongoing imperfections in the latest-generation USB-C standard, specifically with respect to single-source-to-sink interconnect, and encompassing power transfer, data interchange, and both-simultaneously setups.

Nebulous-at-best identified cable capabilities and their user impacts
Polarity dependencies on resultant performance
The broader pros and cons of an industry standard which encourages compliance but doesn’t require independently assessed compatibility

In doing so, I was following up on other points already raised in my prior coverage, based on multiple case studies personally experienced by me.

That includes the necessity for “sink” devices using USB-C for power-input purposes (including charging of embedded batteries) to connect solely to power sources via USB-A-to-USB-C adapter cables, versus newer and more logical dual-ended USB-C alternatives, in order to achieve proper-operation outcomes. Such workarounds presumably result from subpar USB Power Delivery (USB-PD) implementations.

At the conclusion of that prior post, I wrote:

I’ve got one more notable USB-C-related implementation-challenge situation to discuss, but after just passing through 2,000 words, I’m going to save it for next week’s part-two post.

Background to my curiosity

That’s where today’s follow-up blog comes in. Specifically, if you haven’t already figured it out from the title and subhead, I’m going to cover splitters, which assist in interconnecting a single source with multiple “sinks”, again with power, data, or both transfer aspirations.

My main impetus for recent interest in the topic is the portable power stations from EcoFlow and others that I’ve been acquiring, using, testing, and writing about of late. Take, for example, the EcoFlow RIVER 2 that I first covered in detail in February 2025.

It has only two USB-A power outputs, both 12 W max (industry-standard 5V@2.4A, absent any proprietary QC enhancements). And although its USB-C facilities are USB-PD cognizant (5/9/12/15/20V@3A, 60 W max), there’s only one of them. So, if my wife and I both want to fast-recharge our smartphones via USB-C during an extended power outage, for example, how might we be able to accomplish this without arm-wrestling or a shouting match? With a splitter, of course.

Here’s one example of the concept, an early “category creator” market entrant, Anker’s 140W 2-in-1 USB-C to USB-C cable.

We’ll revisit it later in this piece. It comes in 4’ and 6’ length options and black and white color variants and is analyzed in detail in this Reddit thread and linked teardown.

Proportional power allocation (or not)

Back in prior-generation USB days, specifically for power splitting purposes, the implementation and usage were reasonably straightforward. The only source output voltage option was 5 V. The output current was whatever the source max’d out at. And the parallel-connected “sinks” consumed whatever subset of the available electrons each of them could successfully allocate to itself.

The only notable issues (unless I’m overlooking something; readers, let me know in the comments) with this elementary implementation were practical:

Each “sink” device might recharge slower than if it had the source all to itself.
Some of the “sinks” might not work reliably because their available allocated percentage of the current was insufficient for requisite power and/or recharge purposes.
Others might not work because they required a voltage higher than 5 V (Apple laptops, for example, something I learned while researching adapters for part 1 of this series).
And in the opposite-trend direction, if the source was subpar in its design, the high aggregate “sink” current demand might result in excessive output voltage drop sufficient to take all connected power destinations offline.

With USB-C (specifically, USB-PD), things unsurprisingly have gotten a “bit” more complicated. As my colleague Bill Schweber noted in his recent treatise on the topic, “USB-PD allows for multiple loads to be charged at the same time, each with different requirements”. And of course he’s right. But, then again, only with a properly implemented USB-PD ecosystem.

To wit, I’ve also come across plenty of case study examples on Reddit and elsewhere detailing situations, both hypothetical in their proposed root causes and confirmed by postmortem analysis, wherein someone plugged a laptop into one output of a splitter followed by a mouse, keyboard or some other more elementary device into the other output, a second device which (incorrectly) was then also subjected to the first device’s required high voltage and promptly emitted “magic smoke”, followed by demise.

So, what’s a splitter supplier to do? (At least) three options exist, as I see it:

Bail on USB-PD and power everything by 5V@3A only (with already-discussed consequent potential functional issues).
Negotiate with every connect device and run ‘em all at the lowest voltage that they all have in common. Safe? Sure. But also functional interruption-prone with every splitter output-tethered device connection and removal. Want your SSD to power-cycle mid-write each time something else mates with or detaches from the splitter? Me neither.
Or follow the USB-PD spec to the nth degree, aspiring for per-splitter-output voltage and current optimization to the capabilities and preferences of the associated connected “sink” device, and hoping that your silicon and software “building block” suppliers have adequately accounted and compensated for all possible edge and corner cases.

Good luck with that, product developers and users alike.

Selective data directionality

Ready for our next implementation complication? What, if anything, do you do about your customers’ potential desires for the connection between the splitter input and any/all output(s) to transport not only power but also data? In all the product implementations I’ve come across so far (stay tuned for the details to come shortly), bidirectional USB 2.0 (480 Mbps) rates are best-case supported, either assigned consistently to a dedicated output connector or to “the first output to connect to a device,” not simultaneously to all possible splitter outputs. But why?

Keep in mind that, akin to the passive Ethernet splitters that I discussed recently, there’s no active switching going on here. That’s what more complex (and costly) USB hub devices are for, if it’s what you need. Instead, once again, (at least) three implementation options exist with humble splitters, again as I see it (sound off in the comments, readers, if I overlooked or conversely overstated something):

Bail on data carriage and focus only on power transfer. You’ll still need to comprehend the Configuration Channel (CC) signals if you want to support USB-PD, however.
Pick a splitter output and run the bidirectional data solely and consistently between it and the input.
Or decide that the first device that connects to the splitter’s multiple outputs is the only one that has the opportunity, if it chooses to take advantage of it, to leverage not only power but also bidirectional data transfer facilities. And what happens when that device later disconnects from the splitter? Unclear.

Case study implementation diversity

I’ve so far collected four USB-C splitters in recent months, for both personal-use and teardown purposes. As you’ll see shortly, they handle both power and data transfer very differently, a divergence scenario that I find very interesting, as it implies leverage of different reference designs if not entirely different chip-supplier foundations (therefore the teardown angle).

In alphabetical order, beginning with the product you’ve already been introduced to earlier:

Anker 2-in-1 USB-C to USB-C cable
- Length options: 4’ and 6’
- Color options: black and white
- Outputs: 2
- Power carriage: 140 W (max). “When two devices are used simultaneously, the first device plugged in receives higher power. The actual power each device receives depends on its power needs.”
- Data carriage: USB 2.0 (480 Mbps) to first connected device
Belkin 2-in-1 USB C to USB c Cable
- Length: 5’
- Color options: black and white
- Outputs: 2
- Power carriage: 140 W (max). “With two devices, smart power sharing splits power and the first device plugged in may get priority.”
- Data carriage: USB 2.0 (480 Mbps) to first connected device

Baseus Flash 2 in 1 USB C cable
- Length: 4.9’
- Color: black and white
- Outputs: 2
- Power carriage: 100 W (max)
- Data carriage: USB 2.0 (480 Mbps)
  - Note: data transfer is apparently supported only in the latest v2 design. Conversely, with the seemingly initial product version I’d purchased back in September 2024, “Please note that this cable is designed specifically for charging purposes and does not support data transfer or video signal transmission.”

MPATIBY 4 in 1 USB C cable
- Length: 5’
- Color: Black and grey (the version I own: various other options also available)
- Outputs: 4
- Power carriage: 5V-only: “The usb c multi charging cable does NOT support fast charging.”
- Data carriage: USB 2.0 (480 Mbps), consistently and only to one of the outputs, with a uniquely labeled connector.

Online expertise recommendations, and in conclusion

Back in the early days of USB-C, when Nexus smartphones and M1 Apple Silicon-based laptops were getting destroyed by dodgy cables, hubs, chargers and other third-party implementations (or at least that’s what Apple was blaming), an engineer at Google named Benson Leung was the “knight in shining armor” that everyone was relying on to both publicly shame the miscreants and tell users what they should be buying instead. Benson’s seemingly still at Google and remains active on Reddit re USB-C matters, even though his Linkedin profile reports he’s now primarily working on other stuff.

More generally, I consistently found myself directed toward relevant discussion threads on the UsbCHardware subreddit (for which Benson is one of the moderators) as I was web searching while researching various topics in preparation for writing this piece, links to several of which I’ve already shared in both parts of this writeup series. Quality time spent there to get up to speed, while as-usual-for-Reddit filtering out the cruft, is recommended for any USB-C devotee.

And with that, I’ll wrap up for today. As always, I welcome your thoughts in the comments!

—Brian Dipert is the associate editor, as well as a contributing editor, at EDN.

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