Pretty sure it's fine, the third plug is just for earthing/grounding, your old cable was double insulated and didn't require it. It was still there on the old one as plastic to open the shutter in outlets that allow the other two pins to plug in.
Thank you very much. Its amazing to have someone reply so quick. I have used the plug and no problems or issues since. Thank youI have a sony vaio laptop but the plug in it has broke. The original plug was a 5amp fuse ss145/a. And was 250w 2.5v. The replacement plug I found was also 250w 2.5v and a 5amp fuse ss145/a. The plugs are exactly the same but just different branded and the top pin is metal like the other pins unlike the original charger where the top pin is just black. I just wanted to know if this is safe to plug into my laptop. I plugged it in and it works but in the long run is it safe?