When you are trying a new finish, it is better to strip off the old finish completely first. So do a stripping and wax job. If you are doing a top scrub and re-coating only, it is better to stay with the same finish that you already have on the floor.
In most cases, it might be ok to lay a different finish on top of the other, however, in some cases you might see the different shades due to different chemical components in the finish. So, if you do not want to take a chance, use the same brand name finish, if you are doing a top scrub and re-coat. If you want to try a new finish, strip the old finish off completely and lay a new one.