The answer to this question is not as straightforward as you might expect, as it all depends from one model to another. The factors that chime in are the size of the cart, the material that was used to make it and the size of the basket.
While some carts can support up to 50 lbs, others have a total capacity of 500 pounds. This is the reason why you should take a close look at what the manufacturer of the product that you like has to say about the weight limit of the option.
When it comes to the carts you find at supermarkets, the weight capacity of the models that they use also depends. For instance, the carts used at Walmart can support up to 250 lbs. while those that you can find at Costco can hold up to 148 pounds. However, it should be added that some experts argue that the weight capacity of these carts is bigger than the one advertised by manufacturers.