Sometimes there is a difference in meaning with or without "the" -- but not in this case.
"electrical products' is a non-bounded term referring to the entire class of these items.
"THE electrical products" points at some specific items previously mentioned.
If the sentence had said, "Contact us for further information about electrical products." (with no qualifying phrase "in this catalog'), that would imply that the company is prepared to answer all possible questions about all the electrical products in the world, "electrical products" as a class.
Some companies might say just that. The Glidden Paint Company might say, "Contact our Interior Design experts with all your questions about indoor paint" -- setting themselves up as experts on the topic of "indoor paints" as a class.
But that interpretation is not possible because the sentence goes on to limit "electrical products" to those "in the catalog."
That makes "electrical products in the catalog" as specific as "THE electrical products already mentioned in the catalog"
"Ask me anything about dogs" means that I am an expert in the entire set of objects called "dogs" -- dogs as a class, or even "dogs" as a concept.
But "Ask me anything about the dogs" is meaningless -- unless it is understood that we both know which dogs I am referring to specifically.
There is also no difference between "shown in this catalog" and "in this catalog." If the expression were contrasted with some other condition -- say "shown in this catalog" compared to "deleted from this catalog" -- then there might be a difference.
But it can normally be assumed that any item IN the catalog is SHOWN in the catalog, so both expressions mean the same thing.