It depends if it’s an analogue or IP camera and what the power source is.

Analogue generally use 12VDC, some IP cameras as well although nowadays most receive power via Power-over-Ethernet (PoE) which is the network cable feed running to the camera.

There are several reasons why your security cameras may not be connecting to your WiFi. Here are some potential reasons:
Incorrect WiFi Password: Make sure you are entering the correct WiFi password. The cameras cannot connect to the WiFi network if the password is wrong.
Weak WiFi Signal: The WiFi signal may be weak if the cameras are located far away from the router or if there are obstacles between the cameras and the router. This can result in connectivity issues.
Network Congestion: Too many devices connected to your WiFi network can cause network congestion and slow down the connection. This can make it difficult for your security cameras to connect to the network.
Firmware Issues: If the security cameras' firmware is outdated or corrupted, it may prevent them from connecting to the WiFi network.