Let's see result first:
What all we need:
1. ESP12E
2. A normal outlet
3. Power adapter 220V to 6VDC
4. Power module 6VDC to 3.3VDC

1. ESP12E

2. A normal socket

4. Power module 6VDC o 3.3VDC

1. Making wifi communication board

This project uses ESP12E to make wifi communication with house's wifi network. Then, a mobile phone in network can take control ESP12E via local web browser.
Make PCB circuit for ESP12E:

2. Code works:

#include <ESP8266WiFi.h>
#include <ESP8266mDNS.h>
#include <WiFiUdp.h>
#include <ArduinoOTA.h>
//------------------------------for local web
#include <WiFiClient.h>
#include <ESP8266WebServer.h>

MDNSResponder mdns;
ESP8266WebServer server(80);
String webPage;
//----------------------------for local web

const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_PASS_WORD";
int pinout=14;  //for relay
boolean socket_change;

void setup() {
  pinMode(pinout, OUTPUT);
  Serial.begin(74880);
  Serial.println("Booting");
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.waitForConnectResult() != WL_CONNECTED) {
    Serial.println("Connection Failed! Rebooting...");
    delay(5000);
    ESP.restart();
  }

  //Authentication password for programming OTA
  ArduinoOTA.setPassword((const char *)"123");

  ArduinoOTA.onStart([]() {
    Serial.println("Start");
  });
  ArduinoOTA.onEnd([]() {
    Serial.println("\nEnd");
  });
  ArduinoOTA.onProgress([](unsigned int progress, unsigned int total) {
    Serial.printf("Progress: %u%%\r", (progress / (total / 100)));
  });
  ArduinoOTA.onError([](ota_error_t error) {
    Serial.printf("Error[%u]: ", error);
    if (error == OTA_AUTH_ERROR) Serial.println("Auth Failed");
    else if (error == OTA_BEGIN_ERROR) Serial.println("Begin Failed");
    else if (error == OTA_CONNECT_ERROR) Serial.println("Connect Failed");
    else if (error == OTA_RECEIVE_ERROR) Serial.println("Receive Failed");
    else if (error == OTA_END_ERROR) Serial.println("End Failed");
  });
  ArduinoOTA.begin();
  Serial.println("Ready");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  //-----------------------------------------add your code here
  webPage += "<center><font size='27'>ESP8266 Web Server<p>Socket #1 ";
  webPage += "<a href=\"socket\"><mark>TOGGLE it</mark></a></p></font></center>";

  if (mdns.begin("esp8266", WiFi.localIP())) 
    Serial.println("MDNS responder started");

  server.on ("/socket", [](){
    server.send(200, "text/html", webPage);
    // Change status
    socket_change = true;
    delay(100);
  });
  server.begin();
  //-------------------------------------------add your code here
}

void loop() {
  ArduinoOTA.handle();
  //-------------------------------------------add your code here
  server.handleClient();
  if(socket_change)
  {
    socket_change = false;
    if(digitalRead(pinout)) digitalWrite(pinout,LOW);
    else digitalWrite(pinout,HIGH);
  }
  delay(200);
}

Compile the code and download into ESP12E.
Please study how to download ESP12E via wifi, it is very useful for next modify and download. Once ESP12E is installed into socket, it is difficult to take it out.

3. Install to normal socket

This socket contains 3 slot. However, 2 slot have to take out to save space for power module and ESP12E PCB
The power module is taken from mobile phone charger adapter. It's good enough for this project.
Place all things into socket.

4. Testing....

Plug socket into power 220V. Plug into it a lamp for test.