Issue 1:
pd.date_range(pd.Timestamp('2015-1-1', tz='US/Eastern'), pd.Timestamp('2016-1-1', tz='US/Eastern'), freq='H') + pd.DateOffset(days=1)

Traceback (most recent call last):
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/IPython/core/interactiveshell.py", line 3066, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-21-9574a4185a77>", line 1, in <module>
pd.date_range(pd.Timestamp('2015-1-1', tz='US/Eastern'), pd.Timestamp('2016-1-1', tz='US/Eastern'), freq='H') + pd.DateOffset(days=1)
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/pandas/tseries/base.py", line 412, in __add__
return self._add_delta(other)
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/pandas/tseries/index.py", line 731, in _add_delta
new_values = self._add_offset(delta).asi8
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/pandas/tseries/index.py", line 750, in _add_offset
result = result.tz_localize(self.tz)
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/pandas/util/decorators.py", line 89, in wrapper
return func(*args, **kwargs)
File "/home/jeff/.virtualenvs/omnipotent/local/lib/python2.7/site-packages/pandas/tseries/index.py", line 1724, in tz_localize
ambiguous=ambiguous)
File "pandas/tslib.pyx", line 3781, in pandas.tslib.tz_localize_to_utc (pandas/tslib.c:64980)
NonExistentTimeError: 2015-03-08 02:00:00

INSTALLED VERSIONS

commit: None

python: 2.7.6.final.0

python-bits: 64

OS: Linux

OS-release: 3.13.0-61-generic

machine: x86_64

processor: x86_64

byteorder: little

LC_ALL: None

LANG: en_US.UTF-8

pandas: 0.17.1

nose: None

pip: 7.1.0

setuptools: 18.0.1

Cython: None

numpy: 1.10.4

scipy: 0.16.1

statsmodels: None

IPython: 4.0.3

sphinx: None

patsy: None

dateutil: 2.4.2

pytz: 2015.7

blosc: None

bottleneck: None

tables: None

numexpr: None

matplotlib: 1.5.0

openpyxl: None

xlrd: None

xlwt: None

xlsxwriter: None

lxml: None

bs4: 4.4.1

html5lib: None

httplib2: None

apiclient: None

sqlalchemy: 1.0.11

pymysql: None

psycopg2: 2.6.1 (dt dec pq3 ext lo64)

Jinja2: None

Issue 2:
Code Sample, a copy-pastable example if possible

>>> import pandas as pd
>>> idx = pd.DatetimeIndex(['2000-03-26 04:00'], tz='Europe/Berlin') # Switch to DST was on that day
>>> idx
DatetimeIndex(['2000-03-26 04:00:00+02:00'], dtype='datetime64[ns, Europe/Berlin]', freq=None)
>>> idx + pd.DateOffset(hours=-2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/var/local/conda/envs/pandas-debug/lib/python3.7/site-packages/pandas/core/indexes/datetimelike.py", line 510, in __add__
result = self._data.__add__(maybe_unwrap_index(other))
File "/var/local/conda/envs/pandas-debug/lib/python3.7/site-packages/pandas/core/arrays/datetimelike.py", line 1212, in __add__
result = self._add_offset(other)
File "/var/local/conda/envs/pandas-debug/lib/python3.7/site-packages/pandas/core/arrays/datetimes.py", line 832, in _add_offset
result = result.tz_localize(self.tz)
File "/var/local/conda/envs/pandas-debug/lib/python3.7/site-packages/pandas/core/arrays/datetimes.py", line 1151, in tz_localize
self.asi8, tz, ambiguous=ambiguous, nonexistent=nonexistent
File "pandas/_libs/tslibs/tzconversion.pyx", line 276, in pandas._libs.tslibs.tzconversion.tz_localize_to_utc
pytz.exceptions.NonExistentTimeError: 2000-03-26 02:00:00
>>> idx[0] + pd.DateOffset(hours=-2)
Timestamp('2000-03-26 01:00:00+0100', tz='Europe/Berlin')

Problem description

The vectorized operation DatetimeIndex + DateOffset is broken around the DST switching time. However, the same operation works element-wise (Timestamp + DateOffset), so I would expect either both versions to work (preferably) or both versions to fail with the same error.

Expected Output

DatetimeIndex(['2000-03-26 01:00:00+01:00'], dtype='datetime64[ns, Europe/Berlin]', freq=None)

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None

python : 3.7.4.final.0

python-bits : 64

OS : Linux

OS-release : 5.0.0-29-generic

machine : x86_64

processor : x86_64

byteorder : little

LC_ALL : None

LANG : en_US.UTF-8

LOCALE : en_US.UTF-8

pandas : 0.25.1

numpy : 1.16.5

pytz : 2019.2

dateutil : 2.8.0

pip : 19.2.3

setuptools : 41.2.0

Cython : None

pytest : None

hypothesis : None

sphinx : None

blosc : None

feather : None

xlsxwriter : None

lxml.etree : None

html5lib : None

pymysql : None

psycopg2 : None

jinja2 : None

IPython : None

pandas_datareader: None

bs4 : None

bottleneck : None

fastparquet : None

gcsfs : None

lxml.etree : None

matplotlib : None

numexpr : None

odfpy : None

openpyxl : None

pandas_gbq : None

pyarrow : None

pytables : None

s3fs : None

scipy : None

sqlalchemy : None

tables : None

xarray : None

xlrd : None

xlwt : None

xlsxwriter : None