Magsafe Duo not working properly

I used to be able to charge my iphone and watch at the same time. Now, when I charge the phone first, the watch won't charge. When I charge the watch first, then add the iPhone, the watch charges and the phone doesn't. I used a wall charger that provides about 20 watts. I have tried different chargers with the same result.

In summary, I can't charge the phone and watch at the same time.

Any ideas?