Charging speed with cable+adapter to outlet v. cable to wall USB port

The important value is how much current the wall USB port can supply. An iPhone SE can use up to 1.5 amps. If the outlet can supply that or more then that is the fastest the phone can be charged. The cube that comes with the phone can supply 1 amp. If the wall outlet can supply only 1 amp it will charge at the same rate as the Apple cube. Power sources that can supply more, like iPad power sources, cannot charge an SE any faster than a 1.5 amp source.

The iPhone 7 and later can use up to 2 amps, and will charge faster with a 2 amp or higher power source like an iPad power source.

The iPhone X and later have the same limits using a USB power source, but can charge much faster using a USB-C power source which is both higher current and voltage. A USB-C power source can be used with older phones, but will offer no additional benefit as the USB-C source will sense that it is a device that cannot take advantage of the higher power output of the source.

There is no differences.

The power intake is controlled by the iPhone circuitry.

You're welcome.

If there's not enough power than it will not charge, like some weak USB port(s) on a computer.

Lawrence post has a good explanation on charging with your iPhone SE.