Producing XXX(+/- YYY) format in siunitx

I have a class that requires we format uncertainties as X.XX(+/-0.YY).

So far, I can get siunitx to produce uncertainties X.XX(0.YY); however, I do not see a setting in the manual to add the plus-minus sign.

• It would be helpful if you composed a fully compilable MWE including \documentclass and the appropriate packages that sets up the problem. While solving problems can be fun, setting them up is not. Then, those trying to help can simply cut and paste your MWE and get started on solving the problem. – Peter Grill Sep 19 '18 at 0:32

You can modify the output-open-uncertainty:

Code:

\documentclass{article}
\usepackage{siunitx}

\sisetup{output-open-uncertainty = {(\pm}}
\begin{document}

\num{9.99(9)}

\end{document}