Higher power supply wattage uses more electricity?

[IndirectHero]

Does having a super high wattage power supply use more electricity than a less powerful one? Example: 1000 watt power supply vs a 400 watt power supply. Let's say the computer only uses about 350 watt max.

 

[astrofix]

A 1000watt power supply ALWAYS draws more than a 400W.

Depending on how efficient the power supply is the less power it draws.

For example a 80plus Gold certified power supply has a very good 90% efficiency so it draws 10% more than 1000Watts of the grid. 1100Watts in other words. It needs to draw 1100Watts to deliver 1000Watts.

The same goes for a 400Watt PSU. It needs for example 450Watts to deliver 400 Watt.

So a 1000Watt PSU draws roughly double the power of the grid constantly than a 500 Watt even though it is not used and usually disapates as heat or vibration.

because PSU's are more efficient in a sweet spot, then you are not wrong. A larger PSU will be effectively slightly underloaded and so in an attempt to provide 300W might need to pull 340, a 400 PSU might only need to pull 320 provide 300.

So a vastly oversized PSU will therefore be slightly more innefficient, but the difference is small, certainly much less than the cost of 2 PSU over a couple of builds.

Your last sentence is utter rubbish, in the context of a PC needing a certain amount of power i.e. 350W then the 1000W psu does not draw double the 400W PSU.

it will only be slightly more inefficient when idling, but it will more than compensate with better efficiency under full load

 

[astrofix]

best power supply for your system = 1. calculate precise power draw using power calculator
2. add 20% more watts
3. add 100 watts more
4. round the wattage
note: when buying psu calculate wattage by multiplying Amperes with 12, (e.g. '700w' psu has 54A so the 'real' wattage is 54x12= 648) -some (better?) manufacturers would name that unit 650, not 700