Power supplies

How to size a power supply for several GPUs

Adding up rated card wattage and throwing in a hundred watts for the CPU is not enough. A modern card draws twice its rating in short spikes, and those spikes are what trip a unit that looked fine on paper. So the count goes differently: sum the card ratings, add CPU and peripherals, then leave about thirty percent on top.

An example. Two 600 W cards and a 350 W processor give 1550 W on paper. The working unit here starts at two kilowatts, not because the system will draw that much, but because the supply has to survive the peak.

What matters besides wattage

• Card power connectors. New cards take 12V-2x6. Adapters from two PCIe plugs do work, but they add a failure point exactly where the current is highest.
• Single or multiple 12 V rails. One strong rail is easier to plan: no splitting cards between rails and no tracking per-rail protection.
• Efficiency rating. 80 PLUS Gold and Platinum tell you how much energy turns into heat. They say nothing about reliability, which is a separate question about the platform and capacitors.
• Cable length and form factor. In multi-GPU cases the cables have to physically reach, and an ATX unit will not fit a rack chassis.

When two units beat one

Four-card builds are sometimes fed by two supplies with a sync adapter. That adds headroom and eases the load on a single rail, but complicates servicing. For a rack server the better route is redundant supplies inside the chassis: one fails, the machine keeps running.

Send us the configuration and we will size the supply for your cards against real peaks, not catalogue figures.