Can I use legacy chargers with usb-C charging thinkpads?

[likengmx]

I have a new X390 Yoga with USB-C charger.

I have old chargers from my other thinkpads. All 20V, with square connector and round connector (used for X230). And I have bought chinese adapters "square to USB-C" and "round to USB-C" in order to reuse my legacy chargers with the new laptop.I have tried them and they work, charging the x390.

However, later I read that the chargers must be PD protocol compatible, able to negotiate different voltages, and now I'm not sure if I can fry the X390.

Is it safe to use the old chargers?

[likengmx]

Nobody knows? Is it perhaps a question for another subforum?

[axur-delmeria]

IMO the old chargers by themselves are safe, what you should worry about is the quality/reliability of the USB-C converters that you bought, especially if you use them to charge devices that require voltages lower than 20v. The USB-C PD protocol allows the charger and device to negotiate the charging voltage (IIRC it's 5v, 9v, 12v, and 20v), but a shoddily-built converter might fail in a way that 20v is sent to the device regardless of the negotiated voltage.

[likengmx]

I think they are passive adapters. Simple rewiring from old chargers to USB-C. So there are no comms. Always 20V.

My doubt is if a thinkpad x390 or x1 or x13 yoga can demand at some point while charging to lower the voltage, burning something.

[axur-delmeria]

I doubt that they're passive adapters, because you need active electronics to make a proper USB-C device talk to a charger before any charging can take place.

That said, I doubt that the Thinkpad itself would ask for a voltage lower than 20v.

[likengmx]

I think you are right. I didn't see item's description:

Type: DC Converter Plug, PD E-Mark Chip,



E-Mark Chip:



So, I understand these adapters are safe, at least with 20V thinkpads. I don't know what would happend if you connect them to a 5V mobile with a 20v thinkpad power supply.

[zoltan87]

Very interesting, I have been wondering whether these active adapters existed. I have a bunch of Thinkpad power supplies laying around, both the 20v barrel plug variety, and also the older one from pre-T60 era with lower voltage (maybe 16v, I can't remember).

What I have been wondering is whether I could convert those psu units to work with my mother's Surface laptop 4. Anyone has any idea/opinion on the matter?