Pandas, make the bars of a bar graph have equal widths
Looking at the documentation, it seems there is no obvious way.

Looking at the source code of the plt.bar method (held on Axes objects), and searching for uses of the width parameter, it starts getting quite complicated and I don't think it is meant to be used for this purpose explicitly! Lots of internal methods, starting with a _, like self._convert_dx is a clue.

I would just offer a nasty hack for your toy example, hoping it is applicable to your actual data:

In [1] : import pandas as pd 
    ...: import matplotlib.pyplot as plt  
    ...:  
    ...: fig, (ax1, ax2) = plt.subplots(2) 
    ...:  
    ...: pd.Series([0, 1, 0]).plot(kind='bar', ax=ax1) 
    ...: pd.Series([1, 2, 3]).plot(kind='bar', ax=ax2)


Gives



So the hack is to make the length of your datasets the same, adding zeros where needed.