For those unfamiliar, the 18W USB-C power adapter was only available bundled together with the iPad Pro. However the fact that it is now available separately means that you can now buy it if you want an additional charger for your iPad, or if you’re looking for a way to speed up the charging process for your iPhone.
The power adapter is priced at $29 but given that it features USB-C, you will need a USB-C to Lightning cable which is priced starting at $19. For comparison purposes, the bundled power adapter for the iPhone is 5W, so by using the 18W charger, you should be able to recharge your phone at a faster rate.
However we should note that based on Apple’s support document that if you want to truly fast-charge your iPhone, you will need the 29W power adapter at the minimum, which will then allow you to charge your iPhone up to 50% in 30 minutes.