An important tip from one of our users: don't just check total power output, find out what you need in the way of current on each power rail. If you need 20 A on your +12V rails and the supply only has 15A, it doesn't matter how many watts the supply puts out: don't buy it. Make certain that you have ENOUGH rails, too: sometimes, you need more than just two +12V rails for your setup.
Replacing an existing power supply is easier: just get a replacement that meets or exceeds the specifications of the old one. (You can usually find those printed on the side of the supply.)
That said, here's a power supply that is compatible with most ATX format motherboards, puts out 550 watts of power (see specifications for exact distribution). Could this be your next power supply?
ATX12V CompatibleCompatible with the ATX12V standard, the Antec TruePower Trio TP3-550 power supply provides enhanced power stability to drive the latest Intel and AMD processors as well as other system components.
550W Maximum PowerThe Antec True Power Trio TP3-550 provides a maximum power of 550W to deliver safe, reliable output for high-end computer systems.
Highly EfficientDelivering up to 85% efficiency, the Antec TruePower Trio TP3-550 power supply saves energy and may reduce your monthly electric bill too!
Efficient CoolingA low-noise 120mm fan delivers highly efficient cooling for the power supply and the whole system and ensures quiet operation through fan speed adjustments.
Special Fan-Only Power ConnectorsThe Antec True Power Trio TP3-550 power supply features Fan-Only power connectors to control case fan speeds for overall reduced system noise.
NVIDIA SLI CertifiedThe Antec TruePower Trio TP3-550 power supply has gone through a series of rigorous NVIDIA SLI certification tests for maximum system stability when building NVIDIA SLI PCs.
4 x SATA connectors for Serial ATA drives 2 x PCI-E connectors for PCI-Express video cards
Three 12V output circuits provide added system stability Accurate power rating allows TruePower Trio to deliver its full rated power, 24 hours a day rated at 50ºC Fan Only power connectors allow TruePower Trio to control case fan speeds, reducing total system noise Dedicated outputs for stable output and less ripple noise Feedback loop circuits for tighter load regulation (±3%) to maintain accurate voltage to all components Heavy duty protection circuitry prevents damage resulting from short circuits (SCP), power overloads (OPP), over voltages (OVP), and under voltages (UVP) Power Factor value up to 99% Gold plated connectors for superior conductivity