What Happens If the PSU Is Underpowered?

Generally, what happens if a PSU is having trouble supplying enough power to a computer?

A few things, depending on the power supply and how much it is being overloaded. It could refuse to turn on, turn off shortly after powering on, restart, catch fire, explode, etc.

Do you have a specific scenario? Explaining each one is a bit silly.

I don't have a specific scenario. I was just wondering in general. It sounds like the symptoms can be very varied and range from somewhat troublesome to disastrous.

OH I KNOW THIS! Burned out 2 PSUs

Well first, the PSU will run hot. Fan will run at max speed for long periods of time.

PSU will start to shut down in the middle of hard use.
It will refuse to restart until it cools down.

Eventually you begin to smell melting plastics.. then burning plastics.

This is when you HAVE to replace the PSU.


I ran 400w PSUs when it looks like recommended amount was closer to 450w
killed the stock PSU. replaced with freebie. This week replaced with seasonic 650w gold.

Is your psu one that came with a case?

Very important in determining what it might do...

Basically, it depends on the design and implementation of the unit. There are a lot of things that can happen in circuits in overload conditions. They may continue to do what they're rated to do but start to exceed thermal capacity; thermal failures can cause shorts in places, open circuits in others, runaway current effects, current limiting, catastrophic failures like fire and explosions, etc. It could also cause voltage regulation failures in which voltages start to go above or below spec and damage components. The power draw could exceed the capacity of filtration circuits and result in dirty power output, which can also be damaging. Fuses might blow or breakers may trip and the unit might just cut out.

Ideally the manufacturer has graceful handling of these situations that cause protection. Cheaper units will usually fail in much nastier ways.

I had a motherboard failure a few weeks ago that involved power regulation circuitry on the board literally catching on fire. My Seasonic shut down and protected all the other components in the system. Made me very glad to have a solid PSU.