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I wanted to debug an Android-based device (not a cell phone), and connected its USB C port to my computer's USB A port using a cable with USB C connector on one end and a USB A connector on another end.

The computer (an iMac) turned off immediately after I connected the devices. And it seems to be lethal - the iMac seems to be dead since then.

As I later figured out, it was a wrong port to use on an android device - it wasn't a USB C slave data port for debugging/data transfer, it was a USB C PD port for powering other devices.

The Android device is a point of sale system / kiosk, based on Snapdragon 8xx CPU, if that helps. The USB C port I connected to was at the bottom of the device, right where it had a power adapter. It wasn't the device's port at all, but rather the power adapter's port.

According to the USB C spec, it seems that the power delivery is enabled only after some negotiations, but that negotiation happens only between two USB C ports. What happens if I connect USB C to USB A?

And is it possible to resurrect my computer now, or is it dead forever?

Serge Vin
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  • So it turned off does that mean after disconnecting the device your machine doesn’t turn on? – Ramhound Jul 15 '22 at 02:53
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    PD capabilities don't affect other USB features, type C-specific or not. – gronostaj Jul 15 '22 at 05:25
  • @Ramhound, the computer is dead now after that single connection attempt – Serge Vin Jul 16 '22 at 04:33
  • @gronostaj, apparently that's not the case - the iMac (my computer) is dead now – Serge Vin Jul 16 '22 at 04:34
  • Can you edit your question to add some more details on what the USB C device is and what the USB A laptop is? A hypothetical question like this is okay to an extent, but if we know more details we will be more likely to provide useful specifics. – Giacomo1968 Jul 16 '22 at 04:39
  • Have you tried [this process](https://support.apple.com/en-us/HT204267) as explained on Apple’s official site? Look [here](https://www.ifixit.com/Wiki/How_to_reset_the_SMC_on_a_Mac) on iFixit as well. – Giacomo1968 Jul 16 '22 at 04:46
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    added details, @Giacomo1968 – Serge Vin Jul 16 '22 at 04:46
  • I'm not saying it's not dead - I'm saying it has nothing to do with PD. – gronostaj Jul 16 '22 at 06:12
  • USB is designed in such a way that all spec-compliant devices can be safely connected using spec-compliant cables. It doesn't mean that all combinations make sense and will work, but mistakes will be harmless as long as all parts comply with the standard and aren't faulty. Some manufacturers sell noncompliant stuff, eg. type A plug to type A plug cables are used to connect some cheap USB drives, and using these for anything else can be lethal. – gronostaj Jul 16 '22 at 06:18

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Can a USB-C port kill a USB A port? Maybe, but not if everything is functioning correctly.

If you force a USB C cable into a USB A port, it won't be good for either of them, and you'll probably bend and break stuff and maybe short out the port. This shouldn't hurt the computer (other than damaging the port), but if the port is not well designed, it is possible it could damage the computer. But I'm sure this isn't what you meant.

You probably meant you have a cable with a USB C on one end and a USB A on the other end. Can this damage a computer? If the cable is not a valid USB cable, it could. If the cable and USB C port follow USB specs, this is perfectly legitimate and it should not damage anything at all.

As hinted i the comments, your computer turning off could be totally coincidental. Maybe it ran out of power in the battery just at the moment you plugged the cable in, or maybe you bumped the power button while inserting the cable or something else ...

user10489
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  • > "...If you force a USB C cable into a USB A port..." @user10489, interesting suggestions, but no, I haven't forced the USB-C connection into a USB-A socket :) I'm not that powerful. – Serge Vin Jul 16 '22 at 04:36
  • > "...As hinted i the comments, your computer turning off could be totally coincidental..." @user10489, it's not just the computer turned off and that it. The computer is dead now after that. I don't think it's coincidental. And it was not a laptop which could run out of battery - it's iMac – Serge Vin Jul 16 '22 at 04:39
  • but thanks for the comments - i've update the description to add those details – Serge Vin Jul 16 '22 at 04:41
  • Macs typically have especially robust usb ports. – user10489 Jul 16 '22 at 12:12