Power Supply for ESP12F WiFi Module
Most electronic circuits expect CONSTANT VOLTAGE.  Only special loads like LEDs need constant current.  Note that the ESP gadgets are notorious for wanting a good clean and STIFF power source. Wimpy supplies are reputed to cause the ESP to re-boot from supply droop.  The solution to a rather low-current, but STIFF power supply is to use a good size electrolytic capacitor on the supply node.