Second cut, trying to preserve the 120 degree angles, as well as getting proper alignment.

\documentclass{article}
\usepackage{scalerel}

\newcommand\triad{%
\let\savearraystretch\arraystretch
\renewcommand\arraystretch{0}
\begin{array}{c}
\rule{-.01ex}{.01ex}\rule{.05ex}{.8ex}\    \stretchto{
    \scalerel*[\widthof{=}]{\wedge}
    {\rule{1ex}{3ex}}%
}{0.42ex}\    \vphantom{\rule{1ex}{.01ex}}
\end{array}
\let\arraystretch\savearraystretch
}

\begin{document}

$x^2 \triad \begin{array}{c}a\\b\\c\end{array}$

\end{document}

Second cut, trying to preserve the 120 degree angles, as well as getting proper alignment.

\documentclass{article}
\usepackage{scalerel}

\newcommand\triad{%
\let\savearraystretch\arraystretch
\renewcommand\arraystretch{0}
\begin{array}{c}
\rule{-.01ex}{.01ex}\rule{.05ex}{.8ex}\\
\stretchto{
    \scalerel*[\widthof{=}]{\wedge}
    {\rule{1ex}{3ex}}%
}{0.42ex}\\
\vphantom{\rule{1ex}{.01ex}}
\end{array}
\let\arraystretch\savearraystretch
}

\begin{document}

$x^2 \triad \begin{array}{c}a\\b\\c\end{array}$

\end{document}

This can be improved, but first cut is

\documentclass{article}
\usepackage{scalerel}

\newcommand\triad{%
\let\savearraystretch\arraystretch
\renewcommand\arraystretch{0}
\begin{array}{c}
\rule{.1ex}{.8ex}\    \stretchto{
    \scalerel*[\widthof{=}]{\wedge}
    {\rule{1ex}{3ex}}%
}{0.5ex}\    \vphantom{\rule{1ex}{.01ex}}
\end{array}
\let\arraystretch\savearraystretch
}

\begin{document}

$x^2 \triad \begin{array}{c}a\\b\\c\end{array}$

\end{document}

Second cut, trying to preserve the 120 degree angles, as well as getting proper alignment.

\documentclass{article}
\usepackage{scalerel}

\newcommand\triad{%
\let\savearraystretch\arraystretch
\renewcommand\arraystretch{0}
\begin{array}{c}
\rule{-.01ex}{.01ex}\rule{.05ex}{.8ex}\    \stretchto{
    \scalerel*[\widthof{=}]{\wedge}
    {\rule{1ex}{3ex}}%
}{0.42ex}\    \vphantom{\rule{1ex}{.01ex}}
\end{array}
\let\arraystretch\savearraystretch
}

\begin{document}

$x^2 \triad \begin{array}{c}a\\b\\c\end{array}$

\end{document}