Range extender - results are worse than before connecting.

Contrary to popular belief, range extenders don't always make things faster. They can expand Wi-Fi coverage, but this often comes at the cost of speed. Range extenders work by rebroadcasting signals to and from the main router. At a minimum, this will cut speeds in half.

Poor placement of the extender can also hurt speeds. It needs a good signal to both the main router as well as the devices it is serving. And since everything is wireless, radio interference from neighboring networks and other non-Wi-Fi devices operating at the same frequencies are also factors.

If at all possible, try wiring the extender to the main router. This is commonly known as setting it up as an Access Point (AP). You'll have to change a setting on the extender to put it into AP mode. This will be far more reliable and faster. The best wired option is Ethernet, followed by coax and, very distantly, Powerline. Then try placing the AP as close as possible to the wireless devices as you can get.