So, your two 7800GTX cards are on order and will be with you shortly. You’ve just arranged that second mortgage to cover the cost of those cards and so want to make sure they‘re installed in the best possible conditions. You look down into your all aluminium pride and joy, only to realise that the 400 watt “last years super duper best thing since sliced bread” power supply unit probably won’t cut it for you’re latest and greatest upgrade, and so you trawl Google looking for that ultimate, gleaming box of watts – the SLI ready power supply unit.

All fun aside, it is very important that, when considering an SLI or Crossfire (hit retail already!) system, you look at your power supply and make sure it’s capable of the power draw two GPU’s will demand. It wasn’t long ago that a single high-end card would be a power draw concern, but no longer. This is mainly because the power supply industry has introduced an impressive array of high quality PSU’s for us to choose from focusing on +12V performance.

Though this is a roundup focused on SLI, any of these power supplies will obviously be a good choice for high-end non SLI PC’s. Also, there are many power supplies not included in this roundup that are more than capable of running two 7800GTX’s, too.

Let’s begin. I recently came across a handy online wattage calculator called eXtreme PSU Calculator v1.1 which you can find HERE. The purpose of it is to determine a rough estimate of the peak wattage for your system. Peak wattage is the scenario that all your components are consuming there maximum power draw. The reason this calculator uses peak wattage should be obvious – It means that if you buy a power supply that matches or supersedes a systems peak output you should never have any problems under any circumstances. After filling in the online form with the testbeds specification I discovered the peak wattage estimate was 506 watts, so a good quality continuous 500 watt output capable PSU should be right on the money.

I will be looking at four power supplies in this roundup, two of which I’ve already looked at before but previously were tested on a single GPU testbed, so they will be reviewed here again and tested using two 7800GX cards in SLI. The power supplies are the following:

• Enermax Noisetaker 600 watt
• PC Power & Cooling Turbo-Cool 510 watt SLI
• Seasonic S12 600 watt
• Silverstone Zeus ST65ZF 650 watt

I also have the Turbo-Cool 850 SSI from PC Power & Cooling here with me too. This 850w PSU will power pretty much anything you care to throw at it but it doesn’t quite fit in this roundup so I’ll be looking at it in a separate article very soon, so watch this space!