@Aris_Mp - Aris I always find your PSU reviews to be very informative and thorough, but I'm confused over current draw maximums, esp. on say the 12v rail; for instance, this one says 37.5A maximum (I guess I = P/V?), but surely if my house is on say a 15A socket ring main, I'm gonna blow the RCD immediately if it spikes this high on say a high demand graphics card?
You're looking at a switching supply, so power in (current times voltage) = power out times efficiency. So if you're going from 120v down to 12v, you draw ~1/9 if the current out.
Even a basic step down transformer based unregulated power supply will allow much higher currents to flow at lower voltages. It is just a fact of how things work.
It is easy to figure out the amperage from wattage alone. This will not take into consideration efficiency because it just adds more to do.
lets use 120 watts as a base number.
@ 240 volts it would be 120 / 240 = 0.5amp
@ 120 volts that is easy 120 / 120 = 1amp
@ 12 volts it is 120 / 12 = 10amp
@ 5 volts it is 120 / 5 = 24amps
@ 3.3 volts it is 120 / 3.3 = 36.36amps
It is all 120 watts, but you would need larger wires at 3.3 and 5 volts than at 12. This is why computers use the 12 volt rail so much, older ones that did not require so much power made use of the lower rails. This is also why older power supplies may not suitable for modern systems(not enough of the overall power on the 12 volt rail
@nukemaster - thanks so much for your reply; so using your worked example above, a 200W graphics card on the 12V may draw up to (200/12) 17A? But what is this 12V/200W draw at the socket of the PSU? Most domestic ring mains for sockets are say 15A total, so if it was 1/1 the ring would blow straight away? Is the PSU "staging" the huge current draw in reservoir caps to protect the ring?