@dpo 

Try swapping the Ethernet cable the first powerline adapter is using to the router and switch LAN ports. You can also factory reset the wireless adapter by holding the reset pinhole for 5 seconds. 

Another thing to try is to place the wireless adapter in the same room as the first powerline adapter and test both bands. If speeds are normal (obviously) then the outlet you have been using may have come across interference with something else or something changed in the wiring. Move the wireless to a different outlet where it was to see if that helps.

@Tony Many thanks for your reply. I tried all your suggestions: I changed the Ethernet cable between my router and the adapter, and tried all four LAN ports on the router. The results are the same: extremely slow 5GHz wifi. I did a factory reset: same results. Finally, I plugged the extender in a wall outlet in the same room as the adapter: same results also. The 2.4GHz wifi speeds are reasonable but also slower than expected (~30 Mbps download and ~45 Mbps upload while I get ~400 download and ~50 upload when I connect to the router's 5GHz wifi).

Any other suggestions? Did something get fried inside the device?

Thanks.

@dpo 

Remove the Ethernet cable from the first powerline adapter and plug that into your computer to see what speeds that cable is pushing through.

You could also factory reset the wireless adapter by holding the reset button for 10 while the adapter is plugged in, then repair it with the main powerline adapter.

@Tony Using the cable straight from the model, I get 180 Mbps download and 50 upload, but I think those are limitations of the ethernet dongle.

I've already gone through the factory reset twice. No joy.

@dpo 

If you are currently getting 180 Mbps it could give a variable to the reduced speeds. Aside from that, the 5GHz should be giving internet, if it still is not then it would be best to contact our support.