Actually reversing the "phase" of the cap can increase filtering or capacitance depending on how its put in-line with existing caps.
From what I remember:
Adding caps in series [alternating +/-] = increased power filtering potential
Adding caps in parallel [keeing +/- like-for-like] = increased current potential
**Various GPU's need combinations of both of the above.. some only one of the other .. mostly depending on the power phase design and cap choice/layout on the PCB.
Haven't tried mixing polarity yet....
Got a 4v cap mixed in with my 16v pile a couple weeks ago. Got a nice stinky smell and a few minutes later the wife asked me it something was on fire.... "No honey, just pop'n caps in the office"