Neither is "more dangerous"
A switch mode power supply or buck regulator or equivalent may overload if the voltage drops too far as it tries to compensate. The Ohms law bit does not apply.
You will not have enough technical information about all the components in the system. You rely on the manufacturer and they making decisions which are based on their approach to the completed item.
If crude test instruments show .5v variance then probably the peak and trough voltages are significantly greater and lower and outside the spec, i.e you want to measure the ripple and add that to the result. A high level of ripple will be much more significant and damaging.
Also if the regulation is .5v off on any rail then the power supply is probably out of spec. Good manufacturers will try to ensure the electronics works as close as possible to the optimal output voltages (for the cost) irrespective of the input voltage.
The only guide I make is reputation of the manufacturer and look for < 2.5% including ripple.
HiPot testing certificate should also be present. This may reduce the potential for damage from a surge.