I can't see that schematic picture big enough. If it's a forward converter type SMPS, those 2 big caps, should be the supply voltage to the top of primary side, main switching inductor. Are they in series, and they are not sharing the voltage equally ? Is that what you're talking about ? IDK how even they would be new, maybe 40%, 60% voltage split, would be acceptable. But I would not like if only it was 10, 20, 30% of the voltage on 1 cap.
If main's input was 170V rectified, and there's no boost stage like PFC, then maybe it's still not a big deal in series if they are new and rated 250V. IDK, but I would like more equal voltage division, if that's what's you mean. Are you saying 1 cap heats up more too ? Have your checked them with a capacitance meter and ESR meter ?