Made a Cheep Power Supply using Computer SMPS !

I used to do this, maybe about 15 years ago with various power supplies. There are a few good things about such a supply:

• Cheap and relatively widely available.
• Large current/power ratings, multiple useful voltages available.
• 50mV peak-to-peak ripple on 5V, 120mV peak-to-peak ripple on 12V as specified by ATX is much better than most cheap supplies.
• ATX supplies provide 5V "standby" supply, often rated up to 2.5A, so can be used without power up the rest of the rails.

But there are also a lot of drawbacks:

• ATX Specification 240W-per-rail limit not strictly enforced by a number of lower end supplies - can go "pop" if overloaded.
• No current limiting - beefy power supply may put your devices at risk if incorrectly used.
• Horrible efficiency at low loads - they're designed to drive computers which draw 40W+ load, so efficiency at low loads is generally poor.
• Some units are unstable at low loads - they're not designed to run load-less, although this is a bigger issue with older AT type supplies which would chirp/cycle at low loads.
• Bad cross-regulation on cheaper supplies - the voltage rails are not independent nor independently regulated - heavy load on 12V with no load on 5V will lead to both rails going out-of-spec even before reaching the "rated" value.
• Fake ratings - cheap Chinese made supplies often have fake wattage/amperage ratings, so you're not going to get the label output. More than that, they often fail due to bad capacitors on the secondary - so ripple will go out of spec.
• Default connectors not the best for certain uses - Molex plugs are ~6A per contact, SATA plugs are about ~3A per contact. No voltage-drop sensing on most rails except 3.3V, so voltage accuracy is not guaranteed.
• Switching supplies do create RF noise - cheaper models which are poorly filtered will interfere with radio circuits and should be avoided.
• Fan can be quite noisy and not thermostatically controlled. They also wear out, so probably need replacement especially in cheaper models.
• No monitoring of output voltages, currents by default. Easily fixed by using your own meter but adds to the cost.
• No easy on-off switch that is immediate for safety - you can build your own, but while some ATX supplies may have one on the primary, it will take a while for the capacitors to drain.
• Outputs are usually NOT FLOATING - the ground is tied to the AC earth, so seriesing the supply with others may not possible.

So as long as the user is aware, then that's all good, but it's no replacement for a benchtop power supply .

- Gough

I used to do this, maybe about 15 years ago with various power supplies. There are a few good things about such a supply:

• Cheap and relatively widely available.
• Large current/power ratings, multiple useful voltages available.
• 50mV peak-to-peak ripple on 5V, 120mV peak-to-peak ripple on 12V as specified by ATX is much better than most cheap supplies.
• ATX supplies provide 5V "standby" supply, often rated up to 2.5A, so can be used without power up the rest of the rails.

But there are also a lot of drawbacks:

• ATX Specification 240W-per-rail limit not strictly enforced by a number of lower end supplies - can go "pop" if overloaded.
• No current limiting - beefy power supply may put your devices at risk if incorrectly used.
• Horrible efficiency at low loads - they're designed to drive computers which draw 40W+ load, so efficiency at low loads is generally poor.
• Some units are unstable at low loads - they're not designed to run load-less, although this is a bigger issue with older AT type supplies which would chirp/cycle at low loads.
• Bad cross-regulation on cheaper supplies - the voltage rails are not independent nor independently regulated - heavy load on 12V with no load on 5V will lead to both rails going out-of-spec even before reaching the "rated" value.
• Fake ratings - cheap Chinese made supplies often have fake wattage/amperage ratings, so you're not going to get the label output. More than that, they often fail due to bad capacitors on the secondary - so ripple will go out of spec.
• Default connectors not the best for certain uses - Molex plugs are ~6A per contact, SATA plugs are about ~3A per contact. No voltage-drop sensing on most rails except 3.3V, so voltage accuracy is not guaranteed.
• Switching supplies do create RF noise - cheaper models which are poorly filtered will interfere with radio circuits and should be avoided.
• Fan can be quite noisy and not thermostatically controlled. They also wear out, so probably need replacement especially in cheaper models.
• No monitoring of output voltages, currents by default. Easily fixed by using your own meter but adds to the cost.
• No easy on-off switch that is immediate for safety - you can build your own, but while some ATX supplies may have one on the primary, it will take a while for the capacitors to drain.
• Outputs are usually NOT FLOATING - the ground is tied to the AC earth, so seriesing the supply with others may not possible.

So as long as the user is aware, then that's all good, but it's no replacement for a benchtop power supply .

- Gough