May I connect two voltage sources together if they are aprox. the same voltage? (CP2102)
Don't connect both regulators in parallel. Due to mismatch of voltages, current may flow in the direction you don't want.  Even, two linear regulators such as 7805 are never paralleled. Because no two IC/Transistors/Resistors/capacitors are the same. They are never perfectly matched. NEVER. In the absence of explicit authorization from the datasheet...DON'T DO IT. 

Though you can tie grounds together.
@Whiskeyjack explained it in comments.