In Bali and Indonesia you can expect the 2 pin socket and plug as used in larger parts of Europe.
Whether you are staying in a hotel or in a private villa you should be able to get an adapter if you ask for one. The pins are round, not flat or rectangular.
Need an Adapter:
If you come from Australia, Japan, USA, Malaysia, UK, Canada, Singapore, and some countries in Africa you will most likely simply need a plug adapter otherwise the plugs for your electrical appliances will not fit into the "Bali Socket", although the voltage should be o.k.
The standard used in Bali is a two-pin plug (round):
On the picture on the left you can see the standard adapter for Bali, that fits Bali plugs. Because of the 2 pin socket and plug system in Bali you might need a plug adapter (e.g. UK). You can get those at all international airports and once you are in Bali, they can be found in the many small shops that are lining the streets of Kuta, Seminyak, Legian, etc. for a few dollars.
If you bring an adapter from abroad then make sure that it fits into a round socket. There are some adapters that come with a square plug which would not fit into the sockets here on Bali. Because the sockets here are going slightly into the wall, they are not flat-even with the wall!
The Voltage is 230V in Indonesia and Bali.
If the standard voltage in your country is between 220V - 240V you can use your electric appliances in Indonesia and of course Bali.
If you are not sure if this is o.k. for you, check a label on your appliance. It will state the voltage and frequency. If it says 'INPUT: 100-240V, 50/60 Hz', it can be used in all countries of the world. This is mostly in the case of chargers for tablets/laptops, photo cameras, cell phones, shaving machines and electric toothbrushes.
If the frequency of your country differs from that in Indonesia (50 Hz), it is not advised to use your appliance. Be especially careful with moving, rotating and time related appliances like clocks and electric fan heaters.
Power Cuts and Fluctuations
The voltage can fluctuate quite a bit. Not often but regularly you can expect some power cuts that last a few minutes. The more remote you are located the more you should expect that. During high season, when a lot of electricity is needed all over the island for all the AC and so on, the system might shut down a few times per week. But that's no problem at all. Large hotels have back up generators that switch on automatically.Smaller hotels will advise you to shut down AC while they run on back up generator. Otherwise we are sure there will be candles or torches around somewhere where you are.