Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Startup is the most stressful time for a typical switchmode power supply. The output filter capacitors as well as the load must be driven while the input voltage is changing - possibly wildly. With careful design, these factors can be taken into consideration. Not all power supplies are designed carefully or thoroughly tested under all conditions. When power is restored, surges, dips, brownouts, and multiple on-off cycles are possible. This is why it is always recommended that electronic equipment be unplugged until power has been restored and is stable.

Supplies that are autoselecting with respect to input power are vulnerable to voltages at an intermediate value between their low and high ranges. At some values, they may autoselect the incorrect input range:

A subject dear to my heart due to a recent unpleasant experience - Was using a Picturelel videoconference ISDN codec on a job when, because of a powerline fault, the line voltage dropped to 170 volts. The PicTel has a big Onan switchmode PSU which is autoswitching between 100-120 and 200-240 volts. It got confused, and (regrettably) chose the former.... with very smelly results.

Moral: turn off things with cunning PSUs when brownouts occur (oh yes the airconditioner units got very hot and tripped out, too)