It's not an ideal method, but if the voltages are, at DC timing, nominally correct, it's unlikely there's anything else wrong. If a 'scope is unavailable, though, then it's unlikely the problems you mention will be discovered. Aside from that, where would excessive ripple originate? I'd suspect a switching supply if it's an old one, but it makes a great deal more sense to use a battery as a raw supply, or a known linear supply. Now, if you're concerned with noise, and the original MAX232 was noisy, you've got another problem.

However, just to get back to the original issue ... if the device produces the nominal outputs in the DC domain, it's probably not a counterfeit. You have to consider what a counterfeit is. My experience has taught me that, while overseas-originating pharmaceuticals may be manufactured as counterfeits, counterfeit IC's are simply relabeled. They probably won't be of counterfeit manufacture. If it "seems" to work properly, there's probably some unrelated problem.

RE