Doorbell 4 transformer

I purchased the Ring gen2 transformer from Ring U.K. late July this year, my electrician installed it wired to my Ring doorbell 4. The transformer has failed after just 3 months use. Can anyone please confirm if AC or DC output transformer should be used with Ring doorbell 4. Booklet that came with Doorbell 4 says 8-24 volts AC or24v DC, but From previous research I believed it should be 8-24v ACbecause there is no polarity identifiers on the Doorbell 4 wired connections which I now believe are essential for DC connection. The Ring gen2 transformer is 24v DC which I hadn’t realised because believed Ring transformer would be the correct transformer for Ring doorbells. Anyway my Ring doorbell 4 works fine on battery, but the transformer is dead as confirmed by my electrician today. Don’t know where I stand with regards warranty for a dead 3 month old Ring transformer, purchased from Ring U.K.