How do we test 1 V, 40 A power supply. Which load can be connected to test the power supply ?

 

A 25mΩ 40W resistor?
Two of these in parallel
https://uk.rs-online.com/web/p/chas...3685F6B6579776F72645F6170703D3136343433373026

 

I did not know before that they exist low value resistors having high power rating. Yes, having two 50mΩ 25W resistors in parallel, I will have 25mΩ in which the current will be 40 A at 1 V. How abut the power, I guess in parallel the current will be half, like 20 A in each resistor which is like 20 W at 1 V, so it should be fine.

 

I guess I can also have four of 100mΩ 15W in parallel which will have 25mΩ in total.

https://uk.rs-online.com/web/p/chassis-mount-resistors/7547777

 

Whatever you use to connect the resistors in parallel must have a resistance much lower than the resistor value if you want an accurate 40A current.
I'm curious as to what the supply will be used for?

 

Kintex Ultrascale core voltage usually is 1 V and have some tens of current.

 

0.8 - 1.5v at 40 - 100A supplies are not uncommon on high-performance CPU, GPU & FPGA systems - its what the reviewers go nuts about when discussing the latest CPU motherboard or GPU card - usually how many phases in the "multiphase VRM" (voltage regulating module) and the heat-sinking for the same. For overclocking, accuracy and stability of the voltage at full output is critical to taking the CPU to its limit without frying it!

The test rigs for such supplies are usually more sophisticated than resistors, typically some form of linear MOSFET based, MCU-controlled, current sink. 1v at 40A is only 40W so fairly easy to do with a couple of MOSFETs and a decent heat-sink. For example - based on a 1.5kW (50A, 30v) battery tester I built. Layout around the current sense and ADC is quite critical, read datasheets, then re-read several times.