Most of the banks change foreign currencies and deal in travellers' cheques. Some banks do not do foreign exchange dealings on Saturdays. Most of the shopping complexes have a a licensed money changer as well. Most of the major cards are widely accepted by establishments in Singapore. If a shop insists on adding a surcharge then the errant shop-owner can be reported to the respective authorities.
Most hotels can provide a transformer for electrical instruments of different voltage for eg.
SIngapore is a very safe city and staying out late is absolutely no problem if the normal precautions are taken. Local Customs Singaporeans observe certain customs very strictly and it is suggested that the visitor also observes these when in Singapore Do not use first names unless you are invited to. Use Mr., Mrs. or Miss as titles. Obey the laws, as they are strictly enforced. Fines will be levied for such acts as littering, smoking in restricted areas and not wearing a seat belt.