The simplest way is to find a 220V transformer that is reduced to 36V, and use it upside down, that is, connect a socket in the transformer at the primary level, connect the secondary 36V power supply, and plug the charger into the socket to charge. To 36V DC, the 36V AC can be directly rectified, and the DC regulator can be stabilized into 36V after filtering.
Dormitory USB socket charging is slow, because the output current power is too small, so the charge is slow, it is recommended to replace a high-power socket, the output current can be charged fast