This is the safest method.
: While the Power Switch doesn't care about polarity, the LEDs do. If your lights don't turn on, simply flip the 2-pin connector around. Explaining PC Front Panel Connectors
The is a micro-ATX motherboard commonly found in Dell Inspiron 620, Vostro 260, and some OptiPlex 390/790 models (with variations). It uses a proprietary front panel I/O connector — not the standard Intel HD Audio + Power LED/switch pinout found on retail boards.