Iphone 12 charger - Choetech

When i purchased my iphone 12 a month back, the apple store sold me a charger brand called "CHOETECH" , it is a 20Watts charger. The store stated that due to non availability of the apple charger, this brand is the authorized brand for iphones.. Is this true? i notice that my phone takes 90mins to reach to full charge. While, i notice my 2 sisters who use an Iphone 12 Pro & Iphone 11 both their phones get full charged in 20-30mins.. Is this a fault with the charger? I am curious to know whether i have been given the correct information on the Choetech charger.. And how long does it generally take for Iphone 12 to charge to 100%?