I am doing a project right now that uses four SRD-5VDC relays. They switch power from an outlet to the rest of my project. Unfortunately they make a loud click every time they switch. Is there a quieter relay on the market or a transistor circuit that can handle 120V AC switching?
You may use solid state relays (SSR), them being the semiconductor equivalent of a relay. They usually switch AC mains voltage via low DC, usually 3V to 32V (it's almost always printed on their top faces, otherwise check their datasheet). There are also circuits with opto-isolators and triacs that achieve the same result.