The Sun is the source of all energies. These energies stimulate the activities of the houses occupied by the transiting Sun and reinforce or weaken the planetary effects, depending on the Sun's aspect to the natal planet. When the Sun transits an inner planet, it may trigger a dormant aspect between that inner planet and a slower moving outer planet. If a planet is being transited by another planet when it is being transited by the Sun, the effect of the transit is strengthened.
Sun Conjunct Pluto
A Sun conjunction Pluto aspect gives great power and emphasizes extremes of compatibility or in compatibility. There can be great attraction, a need to control, issues regarding sexual taboos, obsessions, or even addictions to substances or sensations. With the Sun person conjunct the Pluto person, there is a greater possibility that an intense situation regarding your partners life purpose is going to weaken your sense of personal control, creating upheaval in your relationship.