What clothes should I pack during the end Mar in Beijing and what kind of adapter power supply will be used in hotel of Beijing?

It is the end of winter and start of Spring in Beijing during the end of March. The temperature will be about 2~12C. There is a sharp difference in temperature between the day and the night.
To visit Beijing, you need to bring warm clothing such as thin jackets and sweaters. Do wear warm enough when enjoying outdoor nightlife. Strong wind occurs sometimes with terrible floating dust and sandstorms. Please remember to prepare glasses, masks and scarves. Well, you can also bring an umbrella. normal shoes are OK.

The electricity in China is generally 220V, 50HZ, AC (Hong Kong is 200V; Taiwan is 110V), while the supply voltage of Japan is 110V, 60HZ.

If you travel to China and wish to bring electric devices for use during your stay, a transformer, which can be bought in China for CNY100-200, is necessary. Most of the hotels in China have both 110V and 220V electrical outlets in the bathrooms, though in guest rooms usually only 220V sockets are available.

As the shape of a socket varies between countries, a portable plug adaptor may also be necessary. It can be purchased from travel stores (such as Franzus) or electronics stores (i.e. RadioShack, Best Buy) in your local countries. Also you can buy it in China.