According to Thermaltake the output power of the PurePower 520W is the following

We utilized the ASUS A8N Premium motherboard with two 7800GTX VGA cards (SLI mode) in all our tests. The ASUS probe utility indicated a really stable performance in idle mode.

Following, we ran all the tests that 3DMark05 offers, to push the VGA cards to their limit. We reran the tests four times, and this is what we got with ASUS Probe.

We repeated the procedure once again, this time with a 3DMark2005. The Asus Probe reports are shown as follows:

It looks like the PurePower 520W maintains an as steady as possible voltage flow. Furthermore, you can see what the SpeedFan reported on voltage stability during these tests.

3.3V

5V

12V

VCore

The following two graphs came from the manufacturer. In the first graph we can see how the rotation changes in accordance with temperature, while in the second one, how the voltage changes as related to temperature.

However, we had a major problem with this P.S.U. In some instances we had immediate system shut-down. That is, no reset/restart but shut-down. We tend to assume that this has to do with the graphic cards that we used. nVidia suggests a minimum P.S.U. that can provide 30A in the 12V rail, and the PurePower 520W offers 15A in the 12V1 rail, as well as 15A more in the 12V2 rail, 30A total. However, it looks like there where stability problems, causing the P.S.U. to shut-down for safety reasons. We had no problem with the PurePower 500A though, offering 18A in each of the 12V1 and 12V2 rails (36A total). We had to look into this a little further, so we carried out the same tests with two nVidia 6800Ultra cards, and we had no problems making continuous 3DMark05 test cycles for 2 hours.