USB-C KVM Switch v3 (with USB Power Delivery / 135watts) does not fast-charge SteamDeck (stuck in 15W mode)

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KVM Model:

USB-C KVM Switch v3 (with USB Power Delivery / 135watts)

USB Interface (5-gigabit or 10-gigbit):

10-gigabit (in fact, both are connected via a Thunderbolt 5 cable)

Problem:

Hi! I have a bit of a situation with charging: I have two devices connected to the KVM: a MacBook M5 Pro and a SteamDeck, that I use for my own development.

For some reason, MacBook has no problems charging from the KVM - it sits at its “I save the battery” 80% all the time, whereas SteamDeck, while indicating “charging” is just slowly losing power over time, forcing me to charge it from a different source.

The ability to keep both devices charging-while-using was kinda the whole purpose of getting the KVM, so some idea to why this may be happening would be very much appreciated.

Other Notes:

Both are connected via a Thunderbolt 5 cable, although of different makes. I have tried swapping the cables (what if one was defective/just bad), tried swapping the ports - to no avail. The situation persists, unfortunately.

Updated post discussion

The KVM supports strictly two power modes:

  • 5V/3A - 15W
  • 20V/3A - 60W

Steam Deck requests a very specific power mode for fast charging: 15V/3A - 45W, and it does not accept higher voltage. Since KVM cannot provide it (whether due to firmware or hardware limitation is not clear yet), the negotiation results in 5V/3A - 15W mode being picked, and Steam Deck slowly losing the charge over time, when the consumption exceeds 15W.

Workaround

For now, I managed to somewhat work around the limitation using this thing (USB C Video Hub NEWQ Typ C Hub 3.2), that has two 10Gbps display ports outputs, with one of them also being a PD port. Steam Deck charger (or Anker, or virtually any decent modern USB C charger) goes into the port with PD, while KVM goes into the port without PD.

The issue is, it is 10Gbps - so it is capped at 2560x1440 100Hz, 8 bit color - or 10 bit, but 60Hz.
It also does not support HDR. As in, it registers the screen as one having HDR, but it doesn’t really work.
I didn’t manage to find any “throughput 40Gbps and add PD” adapters so far, if I find any - I’ll do my best to post one in here. Hypothetically speaking, a Thunderbolt 4/5 hub should be able to sort this out, but they cost upwards of 230$ (and sky is the limit) and it’s not quite something I’d like to spend now, in addition to the KVM price.

It would be nice, if the 15V/3A step was supported by KVM natively to not have to spend 50-ish EUR/$ on a meh third-party workaround - but only @wendell and @Level1_Amber may confirm, if it’s possible. Once that is updated, I’ll update the post as well.

Update on charging step limitation

Unfortunately, this is a hardware limitation of the KVM chipset. So some sort of Thunderbolt 4 (or later) dock for 40Gbps or, well, the cheaper workaround I found is required to get it charging fast.

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A correction here: it does charge the SteamDeck, but its light (yellow) indicates a sub-45W charging mode.

May it be something in negotiation, that prevents it from negotiating full power?

Disconnecting MacBook from the other port entirely does not change the situation.

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I also tried the same T5 cable to connect to a power bricks, 140W, 65W - both gave the “white light” (full power charging) indicator on the deck. Connect it back to the KVM - “yellow light” of sub-45W charging.

Tried another cable, that has worked with the brick for a long time - with the brick, it gives the “white light”, whereas connected to KVM it also gives the “yellow light”.

Could there be an issue with negotiating power delivery with specifically SteamDeck?

Has anyone tried it before and had different results?

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There is different charging protocols for USB PD. It could be possible the KVM does not support what the SteamDeck wants. See if the KVM list what exactly is supported, and match that up with what the SteamDeck supports.

They also make USB C PD diagnostic adapters that you can put inline and it will report what was negotiated.

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It is annoying that listing usb pd voltage isn’t common as there are like 30 different PD voltages. Anytime I see a UL listed power supply it has them listed on the physical device. it would be nice if the l1t store added this info to the listings. I think it was in the description somewhere as being under 20v which was the reason I didn’t get it.

edit actually I looked it up and even the 100w spec has 20v as the minimum so not sure how it’s 135w

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I am considering the in-line adapter.
The ports markings (and the same is visible in the user manual) are 5V/@3A and max power at 20V/@3A - the latter being most definitely above the 45W that SteamDeck marks as the “fast charging” mode.

I can imagine that it may request specifically 15V/3A and the KVM saying “nope” and them both dropping down to 5V/3A . And MacBook saying “yeap, 20V/3A, give it here”.
But without the tester or @wendell himself it would be difficult to confirm.

Do you have any recommendations about which testers/usb C throughput monitors are OK and don’t break the bank?

Overall, this sucks: it was effectively impossible to tell that this would be an issue before purchase of the KVM. I like the KVM otherwise, and returning it would either way put me out of 100+ (80 being just the tax), so yeah…

I mean, the ports list 20V/3A, so I’d imagine, 135W is the combined, not per port charging power.

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Make sure steam decks bios does not enable USB-DRD. Its known to break a lot of USB functionality. Forcing DRD to off (usb mode foced to (o/u/e/x)HCI) is what allowed me to charge my steam deck from my USB hub. KVMs are likely to have similar USB circuitry as hubs.

Disabling USB DRD will not harm the usefulness of steam deck in any way.

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Hm, this is curious, I will check this out.
I’m not sure this would help, but doesn’t hurt to try, since I won’t be using the DRD functionality anyways.

What makes me suspicious it wouldn’t necessarily work is, it does technically charge (technically correct, the best kind of correct), but only in sub-45W mode :thinking:

I’ll try that today and write here the results.

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ok guess i just looked at specs not at all the pictures

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Hi just seeing this thread.

I can confirm per-port power is this:
Port 1 60W / 20V / 3A OR 15W / 5V / 3A
Port 2 60W / 20V / 3A OR 15W / 5V / 3A

BUT

The Steam Deck tries to negotiate 45W / 15V charging. It cannot do standard 60W / 20V. This is very unusual. Most portable devices or laptops will be capable of the standard 60W / 20V.

So, your Steam Deck will drop down to the 5V / 15W charging as its only option. This causes a trickle charging effect during strenuous times (charging and playing a game at the same time).

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Still double-checked, and it’s already in xHCI mode by default.

Thank you for checking it out!

Do you happen to know, whether this is a firmware limitation, or the KVM’s voltage regulator is physically incapable of delivering 15V charging step?

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It’s actually even worse than that: in unloaded desktop mode, when the deck’s system reports <15W consumption, the battery still slowly drains. It drains marginally slower, than completely unplugged, but really, really marginally :frowning:
I saw a similar effect with a 15W power brick - it may be that Steam Deck OLED lies about power consumption, or maybe this is somehow a deliberate choice on Valve’s part in the “unsafe” mode.

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To add to the question @Level1_Amber , if this is a hardware limitation, and thus has to be solved with extra devices, would you perhaps know a USB-C hub, that would be able to pass through the 40Gbps video signal and provide PD from a power adapter?

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This is a hardware level chipset limitation.

Your best (most affordable) bet might be to get a used dell or lenovo dock. A cheap USBC dock probably won’t be TB4 (40gbps) Here’s an Amazon example but you could always try eBay too.

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