I have about 10 computers laying around in various states of operation. Some don't have a power supply. I want to clean up the whole lot and make about 4 usuable computers. My question is to do with swapping power suppies. How can I tell if I can take a power suppy from one machine and put it in another?

Basically, if the power supply is roughly the same size and uses the same plugs as the one in the computer it will replace, it will work, unless a particular computer uses an insane amount of power and you try to put in a lower wattage power supply, then you might start having problems. For a typical computer (single-core processor, a floppy drive, a CD drive and a typical mid or low-end video adapter, 75-100 watts should be sufficient. (This is info I got off the internet. At least 145 watts should be fine. At least 300 watts if this computer has a high-end video card and/or multiple hard disks and a dual or quad-core processor.) Hope this helps, -Trent

Trent, Thanks for the info. The poer supply I am going to sway is 250 watts. So this seams in line with what you have stated. My concern was that I may swap the power supply and fry the motherboard because the power was too much.

It depends on the system specs. Older PCs (prior to the P4 & Athlon) use the +5v rail to power the CPU. Newer systems use the +12v rail. The "75-100 watts" given above is ridiculous...even if it worked, it leaves no margin for error & the PSU would be running at max capacity. Consider 250W to be the minimum you should consider but you also have to consider the hardware being installed & you have to take the voltage rail/amperage ratings into account. There are also different types of PSUs...AT, ATX, mATX. You cannot fry a system by having a PSU that is oversize. If your system only needs 200W & you install a 1000W PSU, the system will only draw what it needs. Have a look at this: Power Supply Myths Exposed! "If my answers frighten you then you should cease asking scary questions" - Jules Winnfield (Samuel L. Jackson) in Pulp Fiction

Your answers are not scaring me. I am just trying to learn as much as I can and make sure I understand you and not get into a situation where what I heard/read is not what you said.

Have a look at these: Choosing The Right Power Supply Everything You Need to Know About Power Supplies If you need more, let me know. I have dozens of sites on PSUs bookmarked because there is SO much misinformation out...such as what you got from Trent. "If my answers frighten you then you should cease asking scary questions" - Jules Winnfield (Samuel L. Jackson) in Pulp Fiction

Too much power is not a problem. PC components will only draw as much as they need. If you have some OEM power supplies in the bunch, you have to be aware that some OEM manufacturers used proprietary power supplies/motherboards with different wiring then standard generic.