I assume that you have tested the powerline adapters with your Mac (with the WiFi turned off temporarily on the Mac) and have connected directly to the "remote" powerline adapter with an Ethernet cable to make sure that you can get a good Internet connection that way.
If you can, then the Time Capsule should work OK. If you can't, you'll need to first verify that your Mac can get a good connection through the adapter before you can set up the Time Capsule.
Assuming that the adapter is working correctly, connect an Ethernet cable from the adapter to the WAN "O" port on the back of the Time Capsule.
Power up the Time Capsule for a full minute
Hold in the reset button on the back of the Time Capsule for 7-8 seconds, then release
Allow a full minute for the Time Capsule to restart to a slow, blinking amber light status
Click the WiFi icon at the top of your Mac's screen and look for a listing of New AirPort Base Station.
Just below that, click directly on Time Capsule
The example below shows an AirPort Extreme as the New AirPort Base Station. You will see Time Capsule on your screen.

When you click on Time Capsule, that will start up Apple's setup "wizard". It will take a few seconds to analyze the network, then display a screen that looks like the example below, except that you will see a Time Capsule pictured.

Network Name.....Type in the exact same name that your existing wireless router is using
Base Station Name.....Type in a device name that you want to call the Time Capsule
Password.....Type in the exact same password that your wireless router uses for the network
Verify.....Type in the same password to confirm
Click Next
The "wizard" will set up everything for you. When you see the message of Setup Complete, click Done and close the window.
The Time Capsule is now set up and also is providing additional wireless range for your network.
Note....because you have changed the settings on the Time Capsule, you will likely have to set up Time Machine on your Mac again to get backups going again. Time Machine will likely start over and make a new complete back up of your Mac, then move forward again with normal backups.