220 volt 50hz is supplied in Bali. A 2 pin plug is required. These adaptors can be purchased inexpensively. Alternatively, borrow from your accommodation reception.
Hint: I always take a power board so i can charge more than one item at a time….so handy to charge phones, cameras, ipads etc.
For short trips, i don’t bother with a Bali sim card anymore.
Plenty of hotels and villas have available wifi, though some are more reliable than others. Most cafes and restaurants have wifi available too – for the cost of lunch or a drink. Just ask for the password.
The free wifi at Denpasar airport is fantastic!