It charges just fine - people have to use higher amp chargers (the provided USB charger is fine), and lower AWG USB cables. Many people are using their cell phone chargers, which don't put out enough amps (most are in the 1 - 1.5 amp range). The Surface 3 wants 2 - 2.5 amps. Also people use their cell phone charging USB cables, which are usually 26-28 AWG cables capable of handling 1 - 1.5 amps. When you use those cables with a 2 amp charger, it will attenuate down to its capacity.
Try using the Surface 3 USB charger with a 24 AWG micro-USB cable. It'll charge just fine, even while using it.