Having a higher wattage power supply isn't a complete waste.
Due to Electrolytic capacitor aging (wattage output from the power supply decreases overtime), it is safer to have a power supply wattage higher than your max load. Cheaper power supplies typically have lower quality capacitors.
Temperature and load effective the life of a capacitor
You could replace the capacitors yourself if you wanted to.
It's like you're moving and the power supply is your vehicle. A low wattage power supply is a compact car and a high wattage power supply is a truck. The truck can handle more and it can make the move easier, but it can be a waste if you don't have too much stuff to move.