Selecting capacitor for SEPIC converter
How can I be sure that the selected capacitor would endure calculated current ripple?


Many capacitor vendors will specify the maximum ripple in their datasheets. 

For example, in this datasheet from Kemet, the maximum ripple current (for 105 C ambient at 100 kHz) is given in the "RC" column:



If you have a ripple voltage requirement, you will have to determine the ripple current from the capacitance value and a little calculus (\$I=C\frac{dV}{dt}\$).

Instead of choosing a badly specified part from EBay, choose one with a proper datasheet, so that you can be sure the specifications meet your requirements.


  I know that ERS is what produces heat in capacitor, but how should I know if some ERS won't produce enough heat to overheat my capacitor?


This will depend on the ambient temperature around the capacitor, how it's mounted to the PCB, etc.

So be sure you understand what conditions the vendor used to specify maximum ripple, and if your specifications are more strenuous (higher ambient temperature, poorer heat sinking), de-rate the part appropriately.