A perforating gun or other downhole tool includes one or more explosive devices that are activable by corresponding one or more initiator devices, such as capacitor discharge units (CDUs). Each CDU includes an explosive foil initiator (EFI) or some other type of a high-energy bridge-type initiator, an energy source (e.g., a slapper capacitor), and a switch coupling the energy source and the EFI or other bridge-type initiator. An electrical cable is coupled to the CDUs for providing a voltage to energize the energy source in the CDUs to provide energy to each EFI. In response to activation of a trigger signal down the electrical cable, the switch is closed to couple the energy source to the EFI.