Thanks for all these details. I bought the first adapter a few days ago and received it yesterday. I will have the 2nd later.
https://www.amazon.com/dp/B08HLSS5T4?psc=1&ref=ppx_yo2ov_dt_b_product_details
https://www.amazon.com/gp/product/B08B1RQRGL/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
I messed around with the FIDI adapter, using only 3 wires (rx tx gnd), but was only able to receive some garbled text even after I tried all 24 combinations. I did:
1. connect all power cords and with PSU on
2. try different pin positions
3. while all this time have the adapter connected to the 2nd computer
4. make sure COM4 is always shown under windows device manager and PUTTY connected
5. I also measured the voltage. The first 3 pins (from left) is ~3.3V higher to the 4th pin.
Did I do something wrong? Should I start all over (power, usb connection etc.) every time switching the pins?