A backpack power supply apparatus, comprising: a battery pack for providing electric energy; a body for supporting the battery pack, wherein the battery pack is detachably connected to the body, the body is at least partially symmetrical about a plane, and the body defines a height in a heightwise direction; a wearable device connected to the body and wearable by a user to carry the body, wherein the wearable device comprises a strap, the strap comprises an upper end connected to an upper portion of the body, and the upper end of the strap applies a force to the body when the user wears the wearable device; an electric energy transmission device for outputting the electric energy of the battery pack, wherein the electric energy transmission device is provided with a first electric energy output interface; and a securing member for securing the first electric energy output interface; wherein an included angle (β) between a projection of a direction of the force on the plane and the heightwise direction is greater than or equal to 30 degrees and less than or equal to 50 degrees; characterized in that the securing member is worn by the user when the user wears the wearable device or is secured to one of the wearable device and the battery pack; the electric energy transmission device comprises a cable, and the first electric energy output interface is disposed at an end of the cable; and the securing member is provided with a first securing slot for securing the cable and a second securing slot for securing the first electric energy output interface, an opening of the first securing slot is smaller than a diameter of the cable, and an opening of the second securing slot is larger than the opening of the first securing slot. a battery pack for providing electric energy; a body for supporting the battery pack, wherein the battery pack is detachably connected to the body, the body is at least partially symmetrical about a plane, and the body defines a height in a heightwise direction; a wearable device connected to the body and wearable by a user to carry the body, wherein the wearable device comprises a strap, the strap comprises an upper end connected to an upper portion of the body, and the upper end of the strap applies a force to the body when the user wears the wearable device; an electric energy transmission device for outputting the electric energy of the battery pack, wherein the electric energy transmission device is provided with a first electric energy output interface; and a securing member for securing the first electric energy output interface; wherein an included angle (β) between a projection of a direction of the force on the plane and the heightwise direction is greater than or equal to 30 degrees and less than or equal to 50 degrees; characterized in that the securing member is worn by the user when the user wears the wearable device or is secured to one of the wearable device and the battery pack; the electric energy transmission device comprises a cable, and the first electric energy output interface is disposed at an end of the cable; and the securing member is provided with a first securing slot for securing the cable and a second securing slot for securing the first electric energy output interface, an opening of the first securing slot is smaller than a diameter of the cable, and an opening of the second securing slot is larger than the opening of the first securing slot.