Reddit mentions of SONOFF RF Bridge, 433MHz Wifi Wireless Switch Remote Controllers Smart Home Automation Module Compatible with Alexa & Google Home

ok, cool, thank you.

Is this the RF bridge you're referring to:

https://www.amazon.com/SONOFF-Bridge-Wireless-Controllers-Automation/dp/B07CWTT8R1/ref=sr_1_5?keywords=sonoff+rf+bridge+433&qid=1572551381&sr=8-5

Yup it is. Its also pretty easy and cheap. Just get a sonoff rf bridge, and some rf switches or plugs.
With the sonoff rf bridge you can just "learn" the rf codes, and combine that with alexa, and now alexa can control the rf plugs/rf switches.

Pro: cheap. very reliable. If internet/wifi is gone, you can still control the plugs with an rf remote.
contra: theyre oneway, so you dont get any information back from the plugs. (like power usage, running time, whatever)

Sonoff rf bridge:
https://www.amazon.com/SONOFF-Wireless-Controllers-Automationb-Compatible/dp/B07CWTT8R1

RF Outlet Plugs (you can get anything that works with 433mhz):
https://www.amazon.com/Century-Wireless-Electrical-Household-Appliances/dp/B01N23GRYD/

But sonoff has also wifi outlet plugs, ao you need no bridge:
https://www.amazon.com/Sonoff-Wireless-control-Compatible-Anywhere/dp/B07DDGVC7B/ref=mp_s_a_1_26?ie=UTF8&qid=1541506877&sr=8-26&pi=AC_SX236_SY340_QL65&keywords=sonoff+wifi

And the famous sonoff wifi switches, which you can connect directly to appliances, such as an 3D-Printer. Or a lamp. ;-) Also dont need a bridge.
https://www.amazon.com/Sonoff-Remote-Control-Compatible-Android/dp/B078GDFYTY/

I for myself have like 50 rf plugs and switches at home since ages, and as alexa moved into the home 2 years ago, the sonoff rf bridge moved with alexa into the house, and is since then controlling everything in the house. ;-)