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The Samsung Galaxy A5 supports not only the Samsung's Adaptive Fast Charging scheme but also USB Power Delivery technology for charging over USB Type-C. We'll see if the Samsung phone can be charged using the Google 18W USB-C Power Adapter which is a USB Power Delivery based  charger that comes with the Google Pixel.

Using a USB Type-C to Type-C cable to direct connect the Samsung Galaxy A5 with the Google 18W USB-C Power Adapter, we can see from the USB Power Delivery negotiations that the Google charger repeatedly offers 15 watts (5 volts @ 3 amps) and 18 watts (9 volts @ 2 amps) to the Samsung phone with a 52% full battery.

The Samsung Galaxy A5 is initially seen to request 15 watts (5 volts @ 3 amps) to which the Google charger complies.

The Samsung phone then goes on to request and establish the maximum 18 watts (9 volts @ 2 amps) power contract to charge faster with the Google charger.

We also observe after that both the Google 18W USB-C Power Adapter​ and Samsung Galaxy A5 keep on cycling the same initial power negotiations for some time.

During initial plug in from 52% battery, the Samsung Galaxy A5 is switched off and starts pulling 1.5 amps current @ 5 volts in the first 10 seconds. As the voltage increases to 9 volts, the phone appears to draw current at 1.4 to 1.6 amps to charge at an average 13.5 watts (9 volts @ 1.5 amps). After 90 seconds, the current suddenly drops below 0.5 amps but immediately goes back up to reach around 1.7 amps @ 9 volts. The current then keeps bouncing between 1.5 and 1.7 amps for about 60 seconds before the phone eventually draws around 5.46 watts (9.1 volts @ 0.6 amps) while the phone is being used. 

The Samsung Galaxy A5 is able to charge fine with the Google 18W USB-C Power Adapter using USB Power Delivery at around the same power level as expected from the phone's own Samsung's Adaptive Fast charger.