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Forum rules require to "be descriptive", take the time to explain the problem you are facing properly.
A question that compresses it's content into the title hardly does. I have an idea what you are asking for, if I'm right, the answer would be "it depends on the nature and characteristic of the sources", e.g. batteries, transformer or switched mode power supply, etc.
I am guessing that "to run" should have been written as "to power". I am also guessing that "sources" are 5V power supplies.
But my guessing might be wrong and "to run" might be "signals" and "sources" might be "signal generators". Who knows?
Why two sources instead of only one source?
frito, I see you are designing with old school TTL circuits and maybe using some low power LDO and you "may be" wondering about paralleling these LDO sources because you are probably driving them with 12V and running very inefficiently and hot.
(This is just from my crystal ball and insight)
Short answer is yes but can you do us a favour and give more details on the explicit problem.