When asking if weightlifters or powerlifters are stronger there are a few things overall you want to have a look at. When you are watching at the gym, it can be a bit difficult to tell a powerlifter from a weightlifter. Both of these are very muscular and sometimes have hulking frames. Powerlifters will often be bigger however, yet weightlifters will have less body fat overall. If you are comparing powerlifters and weightlifters, obviously you will have to take into account that each competitor/ individual is different, and so it depends on the personal strengths. Generally though, powerlifters have more strength than weightlifters do.
This is generally due to the strength training, powerlifters are able to build an impressive amount of muscle and mass. The greater strength and power they have, they will be able to produce more power they have to lift. This makes sense as powerlifting competitions are based entirely on picking up the heaviest weights.
Weight lifters focus more on speed and technique. They do not have to lift the heaviest weight in order to win, however they do need to lift the weight from the ground all the way above their head, powerlifters on the other hand do not, they only need to lift the bar a few feet off the ground and then set it back down.