Thank you Cagey ! Your reply is very useful !In that case, it is telling you that the potato salad has a lot of extra ingredients (in addition to potatoes). Maybe it has pickles, cucumbers, and a special mayonnaise -- or whatever people think would make a potato salad better than the usual potato salad.
I'm not sure I know what ingredients make a potato salad 'loaded'.
'Loaded' is easier to explain when it's used in reference to cars, as in the example in our dictionary's definition of loaded:
5. (of a product, building, etc.) including many extra features, accessories, luxuries, or the like:
The new model sports car is loaded—air conditioning, a tape deck, real leather seats are all included.
from: WordReference Random House Unabridged Dictionary of American English © 2016