Is it okay to charge iPhone 16 with a 240W cable and a 70W charger?

The 70W power supply or charger is fine, but it won't charge the phone any faster than a 30W charger.

Also fine to use a cable rated for 240W if you want, but it is overkill unless you already have the cable and don't want to buy another.

the iphones charge by 5volt dc and a minimum of 1Amp watt == volts * amps

there is no upper limit of how much current your chager is able to provide