How do I check what my psu can handle

[agentsmith101]

I want to check if my psu can handle 20a @ 12v....how do I go about doing it? Sorry for being a nub

 

[LED]

It should have a label on the side or google the model and check reviews. You can also hook it up and download Motherboard Monitor and see how the rails are...

 

[Navid]

This is dangerous! Do not do this if you do not have the right equipment and experience.
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The current flowing through a resistor is :
I=V/R, where I is the current in Amps, V is the voltage (Volts) across the resistor and R is the resistance of the resistor in Ohms.

Say you want to test your PSU at 10A. 12V/10A=1.2 Ohms. So, if you place a 1.2-Ohm resistor between the 12V and ground wires, a 10A current should flow through the resistor.

Before doing anything like that, you have to make sure that the resistor can handle that current.

The power dissipated in a resistor is:
P=V.I, where P is the power in Watts, V is the voltage across the resistor and I is the current through the resistor in Amps.

Danger #1: With 12V across the resistor and 10A flowing through it, the power dissipated in the resistor will be 12V multiplied by 10A = 120 Watts!
This means that you need a resistor that can handle 150Watts (to be safe). If you use a resistor with less power rating, it will heat up and may catch fire!!!

Danger #2: Let's say you buy a resistor that can handle 150 Watts. You turn on the power supply and then attempt to hook up the resistor between the 12V and ground wires on a Molex connector. 10A is a lot of current! There will be a spark as you attempt to connect the resistor. The spark can be very dangerous. Put on safety goggles!

Now, if you succeed in making the connection, you want to measure the voltage of your PSU across the resistor. If it drops more than 5% (if the voltage is less than 11.4V), you have a weak PSU.

To test it at 20A, you need a 12V/20A=0.6-Ohm resistor. The power dissipated in the resistor will be 240W. So, you need a 300W (or more) resistor. The spark is going to be much stronger.


But, seriously, let's forget about all that.
Get a good-brand power supply and you can rely on the rating.
When your PC is under load (running prime95), you can measure the 12V rail voltage and make sure that the voltage does not drop too much.