Collect the four energy tanks in Chun Li, C. Viper, Ryu, and Dhalsim's stages. After collecting those four, go back to Chun Li's stage and defeat her. After getting the password, write it down and restart the game. When you go back to your game after using the password, go to C. Viper's, Ryu's, and Dhalsim's stages again to get another three energy tanks. You can keep doing this as long as the stage can be played again after entering the password.