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I have an OEM power supply unit that is cooked. I'm browsing online to find a replacement and am happy to see that they don't cost too much -- the only thing is they all seem to have varying sizes.

Is it a problem if I get a PSU that is smaller than the original one? This is going in an HP Pavillion a000, it's about five and a half years old -- I don't know if that means anything, I just thought there might be some recent standardized dimensions for PSUs or something. No idea.

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up vote 1 down vote accepted

All the PSUs (ATX) i've seen fit into the same physical space unless they were some kind of custom job. Its the wattages on the units that is key. tally up the max load on your motherboard, cpu, drives, graphics card, etc and for best performance you want to hit about 80% of what a PSU is rated for (aka if your total is like 240 watts your going to want a 300 watt PSU)

To make it simple though just look at what the old one was rated for and get one that matches.

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well it was a 250 W psu, but I looked up the model number and found the dimensions for it -- and then searched for PSUs, and found that none of them matched those dimensions – Carson Myers Mar 24 '10 at 2:14
Long as they are the same type (usually ATX) they will attach into the same space. Only time dimensions might be of concern is if you have some serious space limitations in the case but usually when that happens they aren't using an ATX supply. – Shial Mar 25 '10 at 12:10

Anything over 300W is fine, and a regular ATX power supply is what you want.

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Well other than physical dimentions, as long as it supports what you need (20 or 24 pin motherboard power, chip power, appropriate numbers of molex connectors) it should be fine. Make sure its the same or higher wattage than what you have now. I'd worry a bit about if it'll fit into the bay neatly - open spaces in cases are bad ;p

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