The electricity supply in India operates on 230v, 50Hz, which is the same as in the UK and most of Western and Central Europe. So, electrical appliances from these countries work without the need for a transformer. However, check the voltage of the appliance. If you find that it expects 240 volts only, some, like kettles, irons, or hair dryers may take a little longer to reach their desired temperatures.
Appliances from the United States, Canada, Japan and other countries, which are designed to run on 110v power supply, must not be used without a voltage converter. Using a 110 volt appliance where 220 volt is supplied can damage the apparatus and cause a fire; you would need a voltage converter, not an adapter!
There are, basically, three types of wall sockets in India: Type C (the typical European 2.5 Amp plug), Type D(small 3 Prong - 5 Amp), and Type M (large 3 Prong - 15 Amp). Some older models may look different and if they have an on/off switch, make sure that you turn it order to charge your phone or laptop.
Nowadays, most travelling appliances (cameras, laptops, shavers, and some hair-dryers) accept a wider range of voltages, from 110v to 240v. Therefore, they are adaptable to most countries' supply. However, check carefully the voltage stamped on the device before plugging it into the socket.
If you are travelling from a country with a different plug/socket type, you will need a travel adapter to plug your electrical devices into the available wall sockets. However, most hotels, especially those from the higher categories, will lend you an adapter. Besides, they are quite cheap and easily available in India, the more basic ones costing around Rp 25.
If you are planning a longer trip, or planning to stay at remote rural accommodation, bear in mind that the supply could be unstable (if available) and you would need a voltage stabilizer in the way of a transformer. Surge protection is really important for computers as power surges are common, especially in summer