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Many kinds of electronic equipment use an external brick power supply unit. There are several advantages to this; it keeps heat and noise out of the product, and it reduces the scope of electrical safety considerations, as discussed in What's the reason to make power supplies external?

Nonetheless, despite early home computers tending to use external bricks, desktop PCs soon settled on internal power supply units. Why? What's the advantage of an internal unit that outweighs the disadvantages?

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    \$\begingroup\$ Modern low-power PCs do use an external PSU though, either a laptop supply or a USB supply. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 18 '17 at 23:28
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Desktop PCs already have a chassis, and it already has to deal with containing emissions. The unit as a whole will already need emissions testing and verification. There is really nothing to gain from a external power supply.

On the flip side, now the power supply itself can be made more cheaply since it doesn't need to have a finished case that keeps the user from the high voltage, doesn't radiate on its own, etc.

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    \$\begingroup\$ Also, I think the physical size of most desktop supplies is a bit too big for an external brick format. \$\endgroup\$ – Peter Bennett Dec 18 '17 at 23:15
  • \$\begingroup\$ @Peter tell that to the xbox supplies. \$\endgroup\$ – Passerby Dec 18 '17 at 23:29
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    \$\begingroup\$ Better cooling inside the large chassis with plenty of space for an air intake. \$\endgroup\$ – TonyM Dec 18 '17 at 23:43
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    \$\begingroup\$ And a brick on the floor is an unnecessary brick on the floor. Putting your car engine in a trailer behind the car would keep heat and noise out of the car, but it wouldn't be very elegant for the end user. \$\endgroup\$ – Ian Bland Dec 19 '17 at 0:59
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There are many computer form factors, and only half or less use internal supplies at this point. Dell USFF ultra small form factor pcs use external supplies. Lenovo all in ones use external supplies. Other "computers" like the XBox systems use external supplies. The Asus EEE Pcs and mini/pico ITX systems use external supplies. There is an entire market of power supplies and computers that don't use "traditional" internal supplies.

The only real reason internal supplies are used is because empty space in an otherwise large computer case.

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    \$\begingroup\$ Not to mention that a PSU large enough to run three GTX1080Tis would make for a silly-looking power brick. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 18 '17 at 23:29
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    \$\begingroup\$ Not to mention the 2” diameter cable. \$\endgroup\$ – DoxyLover Dec 19 '17 at 0:31
  • \$\begingroup\$ Note that none of the examples you cite are for physically large systems that have to support power-hungry cards plugged in, like high end gaming graphics. \$\endgroup\$ – Olin Lathrop Dec 19 '17 at 11:42
  • \$\begingroup\$ You mean like the XBox systems or playstation systems all of which tend to be top of the line computers and graphics? \$\endgroup\$ – Passerby Dec 19 '17 at 17:58

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