Rear Fan Slow Speed

hi guys, ive just fitted a new rear fan, advertised as 2500rpm, but its only running at about 650 max, fluctuating sometimes between that and 300! there was an extra lead with it, to plug into its standard mobo 3 pin connecter, which would then split so it not only had the 3 pin connection, but also a 4 pin PSU cable, i think to charge its UV's capabilities. can anyone could help with this slow speed? thanks!

 

problem solved, i did have the available connections for the PSU, fan running at 2500 RPM thanks any one guys