"David G. Johnston" <david.g.johnston@gmail.com> writes:
> Indeed I presume it is. I wonder whether a carefully chosen timezone
> specification on the server would cause this to break since the server can
> be made to report the offset using either convention and so at least for
> some timezone specifications the flipping of the sign would not be required…
AFAIK, "reporting the offset" is always done with the ISO convention.
It's only when trying to interpret a time zone specification that
we consider the POSIX convention (and that's mostly because the
underlying tzdb code does so). This does lead to fun stuff like
postgres=# set timezone = 'GMT+2'; -- read as POSIX zone spec
SET
postgres=# select now();
now
-------------------------------
2022-01-19 13:03:36.000152-02 -- report as ISO
(1 row)
postgres=# set timezone = '+2'; -- read as numeric ISO offset
SET
postgres=# select now();
now
-------------------------------
2022-01-19 17:03:41.722767+02 -- report as ISO
(1 row)
IMO, all these cases are best-avoided legacy conventions.
In practice you should set the timezone using the tzdb zone name
for where you live, e.g. America/New_York.
regards, tom lane