  We compute 10 radiative three-body decays of charged charmed mesons $D^+ \to
P^+ P^0 \gamma$ and $D_s \to P^+ P^0 \gamma$, $P=\pi, K$, in leading order
QCDF, HH$\chi$PT and the soft photon approximation. We work out decay
distributions and asymmetries in the standard model and with new physics in the
electromagnetic dipole operators. The forward-backward asymmetry is suitable to
probe the QCD frameworks, in particular the $s$-channel dependent weak
annihilation contributions in QCDF against the markedly different resonance
structure in HH$\chi$PT. These studies can be performed with Cabibbo-favored
modes $D_s \to \pi^+ \pi^0 \gamma$, $D^+ \to \pi^+ \overline{K}^0 \gamma$ and
$D_s \to K^+ \overline{K}^0 \gamma$ with ${\cal{O}}(10^{-4}-10^{-3})$-level
branching ratio, which are standard model-like and induced by different
hadronic dynamics. Understanding of the latter can therefore be improved in a
data-driven way and sharpens the interpretation of standard model tests. Singly
Cabibbo-suppressed modes such as $ D^+ \to \pi^+ \pi^0 \gamma$, $D_s \to \pi^+
K^0 \gamma$, $D_s \to K^+ \pi^0 \gamma$ with branching ratios within $\sim
10^{-5}-10^{-4}$ are sensitive to new physics that can be signalled in the
forward-backward asymmetry and in the CP-asymmetry of the rate, ideally in the
Dalitz region but also in single differential distributions. Results complement
those with neutral $D^0 \to PP \gamma$ decays.
