# Wattage Versus Amperage?

#### tvl

##### Distinguished
Ok - I'm back with another question:

I took the advice of a couple of individuals and for peace of mind for myself went and purchased an Antec 400 watt power supply (Model SP-400).

I know it is a step-up from what I had previously (300 watt) and will certainly handle my PC needs, but I would like a little more education, if anyone has the desire to explain the following:

In a couple of messages I had seen posted here, it was stated that amperage was just important when selecting a new PS ......... and maybe more important.
Ok, here are the stats from the original Bestec 300 watt PS which shipped with my unit and the new Antec SP-400:

+3.3V +5V +12V1 +12V2 +5V SB -12V

300 Watt 25A 25A 18A 18A 2A 0.8A
400 Watt 30A 28A 14A 15A 2A 0.3A

As you can see, +12V1, +12V2 and -12V are greater on the 300 watt??

300 Watt: +5V,+12V1, +12V2 & +3.3V max output = 288watts
+5V & +3.3V max output = 180 watts
400 Watt: +5V,+12V1, +12V2 & +3.3V max output = 390watts
+5V & +3.3V max output = 130 watts

Once again, you can see the 300 watt surpassed the 400 watt +5V & +3.3V max output by 50 watts??

Now, for someone who is technically minded, please explain what this all means. Just how much better is the 400 watt OR in reality, is there only a small difference in the two?

Tony

#### tvl

##### Distinguished
Note: second post - I tried to make the comparison easier to read!

I took the advice of a couple of individuals and for peace of mind for myself went and purchased an Antec 400 watt power supply (Model SP-400).

I know it is a step-up from what I had previously (300 watt) and will certainly handle my PC needs, but I would like a little more education, if anyone has the desire to explain the following:

In a couple of messages I had seen posted here, it was stated that amperage was just important when selecting a new PS ......... and maybe more important.
Ok, here are the stats from the original Bestec 300 watt PS which shipped with my unit and the new Antec SP-400:

....................+3.3V.... +5V.... +12V1.... +12V2.... +5VSB..... -12V

300 Watt .....25A..... 25A....... 18A....... 18A......... 2A..........0.8A
400 Watt..... 30A..... 28A....... 14A....... 15A......... 2A......... 0.3A

As you can see, +12V1, +12V2 and -12V have greater wattage on the 300 watt??

300 Watt: +5V,+12V1, +12V2 & +3.3V max output = 288watts
....................+5V & +3.3V max output = 180 watts
400 Watt: +5V,+12V1, +12V2 & +3.3V max output = 390watts
...................+5V & +3.3V max output = 130 watts

Once again, you can see the 300 watt surpassed the 400 watt +5V & +3.3V max output by 50 watts??

Now, for someone who is technically minded, please explain what this all means. Just how much better is the 400 watt OR in reality, is there only a small difference in the two?

Tony

#### Flakes

##### Distinguished
apparantly its

watts = volts x amps :? - apparantly that only works in DC systems not AC systems...where is crashman he seems to know what hes on about.

im trying to find a page i read along time ago that explained all this... ill be back.

#### borandi

##### Distinguished
apparantly its

watts = volts x amps

Yup, P=IV (power in watts = current in amps x potential difference in volts). Ahh I remember those old physics lessons for once

#### Flakes

##### Distinguished
Now, for someone who is technically minded, please explain what this all means. Just how much better is the 400 watt OR in reality, is there only a small difference in the two?

No theres a big difference with the two if the antec fails you lose the PSU if the standard one failed then you lose the rest of your system with it..

the main difference is the components on the cheap one the voltage on the lines will vary and as time goes by it will get really bad, as for antec those voltages will stay stable for a lot longer, they will eventually start to go but it'll take so long it doesnt matter.

G

#### Guest

##### Guest
Definition of Watts = Joules/sec

Theoretically this energy flow would be defined, as correctly stated by borandi, by the voltage and the amperage. However, in the case of PSU's you have to consider the continuity of all parameters. Cheap PSU's sadly tend to have a low reliability. Fluctuations of all the above mentioned parameters are pretty common with low quality equipment.

So don't wory about Watts and Volts. Get a high quality PSU.

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