It depends on the wattage of the subwoofers. If you have two 10-inch subwoofers with a combined wattage of 400 watts, they will produce more power than a single subwoofer with a wattage of 400. However, if you have two 10-inch subwoofers with a combined wattage of only 200 watts, they won't produce as much power as a single subwoofer with a wattage of 400. It's important to consider the wattage when purchasing a subwoofer to ensure you're getting the best sound quality.