I spent some time today testing out a couple of RS232 adapters with various bits of Psion software. I wanted to write a quick summary of what works and what doesn't:

Notes

CH340

Seems to work in most places, but DOSBox and DOSBox Staging are very unreliable with it. It's very cheap and up until recently was what I recommended, but as I've tried to use SDBG for debugging on real hardware, I've needed something more reliable.

PL2303TA

Great all-rounder so far! I've been using an adapter by UGREEN with this chip in, and it's been solid.

There's just one problem. Prolific discontinued the chip in 2020. Getting drivers to work in newer versions of Windows is a pain. This won't affect you if, like me, you're not running anything newer than Windows 7. Modified versions of older drivers are out there to make the adapter work on Windows 11. Also, stocks will probably run out in the not-too-distant future. Linux, of course, works fine with it.

PL2303RA

I really wanted this to work with everything. You can get boards very cheaply from AliExpress, and my plan was to create two all-in-one Psion RS232 cables - one with a 9 pin mini-DIN for the older machines, one with a Honda connector for the newer ones. But PsiWin 2.3 won't talk to it.

Conclusion

I really want to be able to recommend a good all-rounder for Psion work, no matter what you want to do with the device. The PL2303TA might well be that, but its EOL status might put people off. The PL2303RA was so close to being perfect, but the pickiness of PsiWin 2.3 has scuppered my plans.

I will update this as and when I test more chips. For now I will stick to the UGREEN PL2303TA and separate cables.