AN AIRLINE FOKKER F100 CREW HIT WAKE TURB; OF UNKNOWN ORIGIN; WHILE ON SHORT FINAL APCH. THE CREW PERFORMED A GAR THEN RETURNED FOR A SUCCESSFUL LNDG.

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I WAS HAND-FLYING VISUAL APCH TO RWY 17C AT DFW AT NIGHT WITH GOOD WX WITH A COMPUTER WIND ON NAV DISPLAY SHOWING A L QUARTERING TAILWIND OF AROUND 010/09 KTS AT 3000 FT. APCH ASKED US OUR GND SPD NUMEROUS TIMES AND KEPT SLOWING US AND SAID WINDS WERE REAL WEIRD THAT NIGHT. WE WERE FOLLOWING TFC ABOUT 4 MI AHEAD. WE WERE CLRED FOR APCH AND WENT TO TWR. TWR CLRED US TO LAND; AND SURFACE WINDS WERE RPTED LIGHT OUT OF THE S. APCH WAS SMOOTH WITH NO TURB. AT ABOUT 300 FT AGL; ACFT BEGAN AN UNCOMMANDED ROLL TO THE R. I TRIED TO COMPENSATE; BUT ROLL CONTINUED. ACFT THEN BEGAN TO SNAP BACK IN THE OTHER DIRECTION. IT FELT LIKE A CLASSIC WAKE VORTEX ROLL. I IMMEDIATELY APPLIED GAR PWR AND CLBED OUT OF THE WAKE. WE WENT STRAIGHT AHEAD; CLBED OUT; AND RETURNED FOR ANOTHER APCH. APCH ASKED US IF WE WOULD THEN LAND BEHIND A B757 ON RWY 17C AND WE POLITELY SAID NO THANKS. WE TOOK RWY 17L AND LANDED NORMALLY. WE DO NOT KNOW IF THE TFC WE WERE FOLLOWING ORIGINALLY WAS AN S80 OR A B757 -- BUT AN UNCOMMANDED ROLL AT 200-300 FT; IT DIDN'T REALLY MAKE ANY DIFFERENCE -- A GAR WAS THE ONLY OPTION. I WILL CERTAINLY TAKE HEED WHEN APCH AND TWR ARE RPTING SO CALLED WEIRD WINDS; EVEN THOUGH SURFACE WINDS ARE LIGHT AND SEEMINGLY BENIGN. WE NEVER WERE BELOW THE GS. SO WHERE THESE VORTICES CAME FROM; I WILL NEVER KNOW.