Maybe I was lucky but the hotels we stayed at in EZE, IGR and GIG all had what seemed to be multi-type power sockets. Round pins, Flat or Angled flat pins all worked.
Re Cash - I changed £400 before we left the UK using a moneysavingexpert website that had a comparison tool on it. We spent most of it on food and transport, but most meals went on the cards. This was for 7 days in Argentina.