These are one of the many smart plugs you can use with Alexa, although be aware, NOT with HomeKit and therefore not with Siri. Down from £25 and I can't find them online any cheaper since Argos sold one at £16.49 before Christmas before immediately going OOS.
I cleared the 3 on the shelf in Cambridge, but didn't ask if they had more stock. (Note these were all for me, and not resale!)
Best of luck!