  The pressure dependence of the structural, magnetic and superconducting
transitions and of the superconducting upper critical field were studied in
sulfur-substituted Fe(Se$_{1-x}$S$_{x}$). Resistance measurements were
performed on single crystals with three substitution levels ($x$=0.043, 0.096,
0.12) under hydrostatic pressures up to 1.8 GPa and in magnetic fields up to 9
T, and compared to data on pure FeSe. Our results illustrate the effects of
chemical and physical pressure on Fe(Se$_{1-x}$S$_{x}$). On increasing sulfur
content, magnetic order in the low-pressure range is strongly suppressed to a
small dome-like region in the phase diagrams. However, $T_s$ is much less
suppressed by sulfur substitution and $T_c$ of Fe(Se$_{1-x}$S$_{x}$) exhibits
similar non-monotonic pressure dependence with a local maximum and a local
minimum present in the low pressure range for all $x$. The local maximum in
$T_c$ coincides with the emergence of the magnetic order above $T_c$. At this
pressure the slope of the upper critical field decreases abruptly. The minimum
of $T_c$ correlates with a broad maximum of the upper critical field slope
normalized by $T_c$.
