# USB-A to USB-C Mysteries **URL:** \ **Category:** In My Humble Opinion\ **Tags:** computer-hardware\ **Created:** [August 25, 2025, 12:21pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453 "2025-08-25T12:21:57Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [August 25, 2025, 7:45pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/21 "2025-08-25T19:45:47Z")
Too bad the EU didn’t specify and test for USB PD too ☹ Or did they? Otherwise the EU is going to end up with a bunch of different chargers that all LOOK like USB C, but aren’t actually intercompatible… ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 25, 2025, 8:05pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/22 "2025-08-25T20:05:30Z")
Year. Plenty of Apple devices now have a USB-C-shaped connector. That won’t _reliably_ take power from anything but an Apple-branded cord connected to an Apple-branded power source; be that a wallwart or a connector on another device. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 25, 2025, 8:19pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/23 "2025-08-25T20:19:34Z")
> [@pjd](#): > > The combination of a USB-C to USB-A cable with a USB-A to USB-C converter, or a “dongle,” works because the converter’s resistors trick the device into expecting legacy power levels. > [@Reply](#): > > But, as you saw, many cheaper USB-C devices do not support USB-PD, even if they have a Type-C port, and so no power gets sent at all… and yes, using a C to A to C setup will “fool” the devices into supplying legacy USB power, as the AI said and you already confirmed. These are almost certainly what’s going on here. I’ve seen the same behavior myself. Why the manufacturers couldn’t be bothered to put in a couple of extra resistors is beyond me. The cost is utterly negligible, so it must be laziness. There’s probably a C-to-C cable available with the resistors installed, or maybe has active negotiation on both ends, but I wouldn’t know where to find it. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [August 25, 2025, 8:50pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/24 "2025-08-25T20:50:39Z")
> [@LSLGuy](#): > > Plenty of Apple devices now have a USB-C-shaped connector. That won’t _reliably_ take power from anything but an Apple-branded cord connected to an Apple-branded power source Hmm, that isn’t my experience. My Ipad has been happy charging from any USB-C I plug it into, which includes just about anything _other_ than Apple labeled charging bricks. I’ve used chargers ranging from Google USB-PD, name brand third party ones, off brand third party ones, old USB-A chargers I found in a drawer, and my wife’s 100watt USB-PD MacBook Pro brick. Dell is the one that gets me. The computers seem fine, and are willing to accept power from anything that does 20volt USB-PD. It is the supplied “USB-C” 130 watt charger. It is not actually USB-PD. Anything other than a Dell laptop only gets 5volts 500mA. My Dell laptop is very happy running on my wife’s MacBook Pro charger, but not at all the other way around. ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [August 25, 2025, 9:12pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/25 "2025-08-25T21:12:10Z")
> [@echoreply](#): > > Hmm, that isn’t my experience. My Ipad has been happy charging from any USB-C I plug it into, which includes just about anything _other_ than Apple labeled charging bricks. I’ve used chargers ranging from Google USB-PD, name brand third party ones, off brand third party ones, old USB-A chargers I found in a drawer, and my wife’s 100watt USB-PD MacBook Pro brick. Same as my case with iPhones. Which I would expect, considering Apple hadn’t been including the wall-wart in the box for iPhone since the last generations of Lightning port devices so they were leaving it up to you how to plug it to the mains. May not be as fast as an optimized unit, but it charges. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [August 25, 2025, 9:40pm UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/26 "2025-08-25T21:40:52Z")
And to chime in, my MacBook Pro has a nice magport charger that came with it. But it’s also happy to accept charge from any modern USB-C charger that delivers at least 45 watts. (It prefers 65 watts.) I love that i have one smallish (Dell, i think) 65 watt charger that i can use for my phone and any of my laptops except the big Dell that wants 100 watts. Why yes, there are currently 4 laptops in the house that i use, although I’ve belongs to my employer and I’ll ship it back when this gig ends. And all of them can be charged by the third-party brick i purchased recently. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [August 26, 2025, 2:31am UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/27 "2025-08-26T02:31:36Z")
> [@puzzlegal](#): > > MacBook Pro has a nice magport charger that came with it. But it’s also happy to accept charge from any modern USB-C charger Interestingly enough, on newer Macbooks, the MagSafe 3 cable _also_ speaks USB Power Delivery, and the included charger is just a regular USB-C PD charger. The other end of that Magsafe cable is USB-C. > **[Quick & Easy | Latest Teardown of Apple USB-C to MagSafe 3 Cable (2 m)](https://www.chargerlab.com/quick-easy-latest-teardown-of-apple-usb-c-to-magsafe-3-cable-2-m/)** > > https://youtu.be/kCD6R8k9kqA > > > > > You can buy it on Amazon: https://amzn.to/3EJL2Gm > > > > If you wanna buy the tester of POWER-Z, you can visit our Amazon store: Click here. > > > > Introduction... I’ve also had good luck charging my Apple devices (three Macbooks, an iPhone, and three iPads across different timeframes) with third-party (usually Anker) USB-PD chargers, as long as they were of sufficient wattage. Their [GaNPrime](https://www.anker.com/ganprime) chargers are some of the best available… GaN is gallium nitride, which when used in chargers, allows their size to be drastically reduced (see [Wikipedia](https://en.wikipedia.org/wiki/Gallium_nitride#Transistors_and_power_ICs)). I don’t think any US company comes close right now; even Apple’s own GAN chargers are much bulkier, heavier, and don’t offer as many ports. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [August 26, 2025, 2:44am UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/28 "2025-08-26T02:44:40Z")
> [@Dr.Strangelove](#): > > Why the manufacturers couldn’t be bothered to put in a couple of extra resistors is beyond me. I think some chip (or at least software) has to actively negotiate it, no, even with a cable capable of carrying it? [The Basics of USB Power Delivery Negotiations | Acroname](https://acroname.com/blog/basics-usb-power-delivery-negotiations) It’s a series of back-and-forth requests between the charger and the “sink” device. There are also logical conditions to take into account, like if you want to switch the source and sink (i.e., your phone can actually try to charge your laptop if you ask it to), or if your charger has to change power profiles when more than one device is plugged in. While not crazy expensive, it’s also not completely trivial. My personal gripe isn’t that some devices don’t support USB-PD… that’s fine… it’s that they made the USB-C “standard” actually just the physical connection and not the accompanying usage profiles: not just whether (and how fast) it can charge, but what data speeds it supports, whether it supports DisplayPort Alt Mode, various audio codecs, daisy-chaining, Thunderbolt 3/4/5… they ALL look like “USB-C” but they’re all totally different. I think I’d much rather have different types of cables & connectors, knowing that it’ll “just work if it fits”, rather than twenty different connectors & cables that all look the same but don’t work together. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 26, 2025, 3:10am UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/29 "2025-08-26T03:10:19Z")
> [@Reply](#): > > I think some chip (or at least software) has to actively negotiate it, no, even with a cable capable of carrying it? I’m not _quite_ knowledgeable about the protocol to say for sure. The early versions of USB just had various resistor configurations on the data lines, and the device would just detect this and change the charging limits to compensate. USB-PD, as you say, has a whole active protocol to negotiate the power delivery. But lots of devices don’t need USB-PD! The problem is that they then can’t see the host device at all. As far as I know, adding the resistors would not interfere with USB-PD devices but they would allow non-USB-PD devices to work on those ports. They wouldn’t necessarily get high-speed charging but they’d get _something_, like 1A @ 5V. I have a CO2 meter with this problem; it charges with a C-\>A cable but not C-\>PD. It doesn’t need anything special, power-wise, and I don’t blame them for not including a PD protocol chip. The PD charger I have should have made it work. ---
**Author:** ![DETXL](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/detxl/32/19366_2.png) [@DETXL](https://boards.straightdope.com/u/DETXL)\ **Post date:** [August 26, 2025, 7:32am UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/30 "2025-08-26T07:32:04Z")
> [@Reply](#): > > The whole GMRS handheld market is a mess. I eventually just gave up and made sure to remember to carry the extra USB-A-to-C chargers. I have to psychologically trick myself into remembering “nevermind how it looks… these are not real USB-C…”. I went through what is, I imagine, the same thought process, namely: 1. Oh, it’s convenient that they charge over USB-C; I don’t have to bring so many things with me. 2. …Why isn’t this charging? 3. …For Christ’s sake. Does anybody have a USB-A to USB-C cable? 4. …Is there anything else in this price range? No? Well, bringing a USB-A charger it is, I guess. (I am to understand the other reason people like Baofeng is because they are, or maybe were, modifiable in firmware to transmit on other frequencies, but I only have a GMRS license so I did not endeavor to find out) > [@Reply](#): > > I don’t think those USB-C data blocker “condoms” would work in this scenario, right? I’m not sure. Some kind of dongle is certainly possible, but I imagine it would need to have the right kind of Power-Delivery negotiating circuitry. I have a couple of cables, one well-behaved device (USB-C port, charges off USB-C), and one poorly-behaved device (USB-C port, only charges off USB-A) to test. The well-behaved device draws 15W (5V@3A) whether it’s connected over a C-to-C cable or an A-to-C cable, so I imagine that its charging circuitry just tries to get three amps at 5 volts no matter what. That is also the maximum [the USB-C standard](https://en.wikipedia.org/wiki/USB#Power-related_standards) allows at 5 volts. Whether your average USB cable has an appropriate wire gauge for that current is another matter. The poorly-behaved device will not charge over any C-to-C cable, no matter what charger I use or what inline voltage tester I use, so those dongles (at least) are not willing to do the task of negotiating on my flashlight’s behalf. That said, if it’s connected to a USB-A source it also draws ~.7A at 5 volts. That is higher than the 500mA allowed by USB for normal devices, but lower than the 1.5A allowed for devices conforming to the Battery Charging specification, which Wikipedia summarizes thusly: > The charging device identifies a charging port by non-data signaling on the D+ and D− terminals. A dedicated charging port places a resistance not exceeding 200 Ω across the D+ and D− terminals. I haven’t tested whether or not the flashlight does this, and I’m not sure how high my hopes are for the device being compliant anyway. It’s a nice, bright flashlight with weather sealing so I don’t want to dismantle it to see, but when it inevitably dies I will check back in here 😉 > [@LSLGuy](#): > > Year. Plenty of Apple devices now have a USB-C-shaped connector. That won’t _reliably_ take power from anything but an Apple-branded cord connected to an Apple-branded power source; be that a wallwart or a connector on another device. Chiming in to say that isn’t my experience with my laptop or iPhone, which will take USB-C power from anything over a USB-C to USB-C cable or, in the case of the laptop, the Magsafe cable. They will also charge happily, if more slowly, off my USB-C power banks. _However_, the Nintendo Switch technically has a USB-C port, but my experience has definitely been that it will only output HDMI and charge over that port if power is delivered through a Nintendo-branded power adapter. That could just be coincidence, but it is known that Nintendo overloaded the USB-C protocol on the Switch 2 to include some kind of authentication that [breaks 3rd-party docks](https://www.theverge.com/report/695915/switch-2-usb-c-third-party-docks-dont-work-authentication-encryption), so it is certainly possible for big companies to be _extremely_ poorly behaved when it comes to “connectors that look like, but are not, USB-C.” > [@echoreply](#): > > Dell is the one that gets me. The computers seem fine, and are willing to accept power from anything that does 20volt USB-PD. It is the supplied “USB-C” 130 watt charger. It is not actually USB-PD. Anything other than a Dell laptop only gets 5volts 500mA. I sometimes wonder if this is a holdover from companies wanting to deliver more power to their laptops before the newer PD standards caught up. I recommended someone buy a ThinkPad, which has a proprietary power connector, under the mistaken assumption (as an Apple person) that it would also allow charging over its USB-C/Thunderbolt ports in a pinch. It does not. (Sketchy-and-or-innovative entrepreneurs have designed dongles that let you connect a Power Delivery charger to the proprietary adapter, but there is also evidently circuitry going on there, because you have to be careful to select the right dongle or the laptop will reject it. That said, the dongle does work, eventually) ---
**Author:** ![The\_Librarian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_librarian/32/402_2.png) [@The\_Librarian](https://boards.straightdope.com/u/The_Librarian)\ **Post date:** [August 26, 2025, 8:34am UTC](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453/31 "2025-08-26T08:34:38Z")
USB is supposed to be a standard. And mostly it is. But there are myriad cables and devices where only parts on the standard is implemented. On my docking station there lives a cable that does almost everything USC promises. 100W Power, 2,5G Ethernet, 4K monitor, mouse, keyboard, audio. All through 1 cable. It’s practically magical. but does that cable charge my headphones? Nope. [Previous page](https://boards.straightdope.com/t/usb-a-to-usb-c-mysteries/1022453.md?page=1)