Is it optimized to design same temperature for several heat sink in a power supply?
I am making the assumption that by optimal you mean in terms of reliability and longevity. The amount of heat sinks you use does not necessarily matter. In fact, I would argue that the PCB layout should be the ultimate factor in how many heat sinks you use. Heat sinks are a preventative measure. It doesn't really make a difference if you separate each heat sink for each component or if you use a larger heat sink so long as your calculations and testing show that the temperatures stay well within the optimal component operation range. Just off of experience I would say that it would be better to use a larger heat sink for economy reasons provided that the components are near each other on the layout. What kind of heat sink you need and if you need to include other cooling features (such as a fan) will be determined by the calculations done beforehand. Here I have linked a video by Dave from EEVblog that should assist you greatly if you are having any difficulties with thermal design.