@AVLfilm 

Thanks for all the thoughts in this thread. I had to change our WiFi password after setting up a new Xfinity modem/router. Xfinity decided the special symbol (a pretty normal one) I used in my WiFi password is no longer on their list of acceptable symbols.  So, I changed the WiFi password.

I'm dealing with what everybody else here is dealing with.  But I think I'm doing something wrong.  I hold the device reset button for 5 seconds and the lights blink but other than adding a new device to the Kasa app, I don't see how to enter the new password.

Or, is the idea to remove one of my many devices, add it like a new device, and I'll be asked to enter the new password and, after that, all the other TP-Link devices will work?

It sounds like there is a solution other than manually removing and adding each device separately. I'm just having trouble understanding how to do that.

Sincere thanks, everybody (anybody!).

  @cgulls  . . . also, how do reset a lightbulb?  The smart plugs have reset buttons but the bulbs don't. 

Thanks!

  @cgulls Sounds like you're only doing half of what you need to. After you hold the device reset button for 5 seconds and the lights blink, click + like you're adding a new device. Connect to the device following the instructions on your screen. Then choose "Do Not Reset". Choose the new wifi network and enter password. That's it. It might automatically update the firmware on the plug too.

  @AVLfilm To change the WiFi password for TP-Link plugs in the Kasa app, you still need to reset and reconfigure each device. As of now, TP-Link hasn't added a way to change the WiFi password directly in the Kasa app without resetting. This was mentioned by a TP-Link employee in 2019, but no update has been made since then.

  @AVLfilm 

This didn't work for me. I still cannot connect. I also didn't get any of the promts that was listed in the "solution". I just want to connect to a new modem. Why should it be this difficult?

The app may give you hints on how to reset when you select the device type.  For example: for the HS300 power strips, the "reset" is labelled on the power switch on the bottom -- but that doesn't actually do it.  When first turning the power on the strip, while the circle-light is blinking, press one of the individual power buttons on the strip.  That should reset the Wifi on the whole device so you can then re-add it back into the app.

FYI:  If you have changed to a newer WiFi hardware, know this:  Kasa devices not only are restricted to 2.4Mhz band with WPA2 security, but the bandwidth must be only 20Mhz wide -- they don't play nice with 20/40 widths (which usually defaults at 40).