Have run into that exact thing also, not that the sockets were 5-15R but IEC C13 in a rack CDU. But someone had some adapter pigtails from C14 to a standard NEM

Have run into that exact thing also, not that the sockets were 5-15R but IEC C13 in a rack CDU. But someone had some adapter pigtails from C14 to a standard NEMA socket, of course that doesn't change the voltage at all. Hilarity ensued.