I tried a lot of methods before, but nothing worked. This one is easy, no programming skills needed, just a bit of patience.
The new Broadlink RM Pro hub works with X10 and Alexa.
This little hub is very powerful, also blasts IR signals, so it will control a lot of devices nearby (line of sight for IR)
The Hub learns RF codes. Once you go trough the process of creating all your codes (A1_ON, A1_Off, and so on) using BroadLink "e-connect app" (iOs and Android but no windows) then install "RM Plugin" app (Android only, paid app) RM will translate the commands as a Philips Hue that can talk to Alexa.
All set up is done using apps (no computer interface) and codes, scenes and macros are cloud storage.
I am very happy, finally all the X10 switches and plugs are working with Alexa.
What you need:
1) Your X10 gear (X10 HR12A PalmPad Remote Control to teach RF codes back to the RM Pro) about $14.
2) Broadlink RM Pro (The pro is the one with RF capabilities) about $37 on Amazon. Update to latest firmware.
3) Broadlink "e-Control" App (free, for your smartphone)
4) "RM Plugin" app, $2.49 annual subscription. RM plugin ideally installed in a stand alone power plugged android tablet or phone, since it needs to be running all the time (I used an old tablet, but a cheap android prepaid phone will work)
5) Alexa Device. (Echo, Dot, etc.) Dot is about $50.
Youtube tutorial. Search for "Control practically anything with Alexa" by Paul Hibbert