What is a VRM card for?

VRM cards are "Voltage Regulator Module". They are used primarily in IBM computers/servers. The VRM card sits into a channel attached to the motherboard (similar looking to an IDE channel), and its function is to stabilize voltages to the CPU(s). Often these servers have more than one CPU.

Usually with IBM servers if one power supply fails, there is a secondary power supply unit ready to feed the server components (sort of like a back-up). The VRM card regulates these power supply sources. (yes, many servers are accomodated with 2 or more power supplies and are hot-swappable).

Ok thanks. The reason I asked is because my optiplex gx400 has one.