The sign of a planet describes primarily the STYLE of how that planet expresses it's energy.The house of a planet describes primarily the AREA OF LIFE in which a planet expresses it's energy.
Jupiter in Leo in the 10th (a very flamboyant placement) will express itself very differently from Jupiter in Capricorn... Jupiter in Cap folks tend to approach learning, belief, journeys, and growth, in an organized, practical, pragmatic, and responsible way. Jupiter in the 10th simply indicates that your career, or reputation, will have jupiter-like qualities to it... Like learning, teaching, idealism and travel. This as well as joy and abundance, which is also associated with Jupiter.
Between Jupiter in the 10th and Jupiter in Capricorn, one is not necessarily 'stronger' then the other one. They are just expressed in different ways. Jupiter in Capricorn is more Cap-like in how it expresses itself (sign qualities), and Jupiter in the 10th has a bigger influence on your actual career (area of life).