Not a historian but it's my contention that the idea of "one wage earner supporting a family" is a result of a post WW2 "bubble" of prosperity that Americans enjoyed and popularized as the ideal (aka nuclear family). And that this bubble basically burst in the 1970's leading to a return of both of parents "working".
So was the "single wage earner" the norm in pre-WW2 times?
Women in the workforce prior to WWII typically only stayed in the workforce until they were married (this also varied by class, of course, a higher class woman would likely not work much at all). In 1890-1900, 75% of employed women were single and less than 10% were married. For context, however, only around 35% of urban single women (16-24) worked outside the home (the rest more than likely worked in their parents' home), so it is not as if the participation was massive. Worth noting, however, that the trend of increasing employment of married women predates WWII a bit -- in the late 1920s, the percentage of the female labor force that was married was 25% (up from the previous 10%).
Source:
The Work and Wages of Single Women, 1870 to 1920, Claudia Golding: https://dash.harvard.edu/bitstream/handle/1/2643864/Golding_WorkWages.pdf?sequence=2