Portable power supply

A portable power supply, comprising:

• a) a slender casing, having a compartment disposed along an axial direction, and at least one set of anode and cathode contact points disposed in said compartment for electrically connecting a battery to define a power supply terminal;
• b) a DC-to-DC voltage booster circuit, installed on a first circuit board and disposed in said casing for boosting a low-voltage current outputted by said battery to a 5V DC power;
• c) a USB output socket, disposed along the axial direction of said compartment and being in a female connector configuration, such that a port at an opening of said USB output socket being disposed at a front end of said casing, and a first pin disposed at an internal side being electrically connected to said first circuit board for obtaining the 5V DC power outputted by said voltage booster circuit, so as to supply power to a USB plug connected to said USB output socket;
• d) a protruding USB input plug, installed at a rear end of said casing and plugged into said USB socket for obtaining a DC power to charge said battery;
• and
• e) a charging control circuit, installed on a second circuit board for fixing and electrically connecting a second pin disposed on an internal side of said USB input plug, and said second circuit board including a conducting wire and being electrically connected with an electric conducting contact point on said first circuit board, so as to charge a secondary battery installed in said compartment.