Usually on a brick you'd match voltage, connector and polarity. Amperage would dictate total wattage. Otherwise if those all line up if it fits it ships.
You'd give up power headroom for a smaller unit, some of the larger bricks are like 180-220w, which is needed since you're using higher end stuff like a dedicated GPU. Without sufficient wattage the laptop won't charge the battery or won't have sufficient power to run the laptop.