So I picked up the cheapest ATX PSU I could find on Amazon that was Prime Eligible. It is listed as a KDMPower MIPC 775w and as of 09/30/2018 was selling for the low low price of $15.57 with free 2 day shipping (for Prime members). I'm sure the wattage claim is pure BS, but lets see how bad (or good) it is otherwise.
The Packaging is about as basic as you can get, a plain cardboard box with the PSU wrapped in bubble wrap and a power cable inside:
Looking at the PSU itself, this is a non-modular unit with a 120mm fan and basic black paint job:
The Label is even more ambitious than the product listing page, claiming 875W
:
Lets take a look inside:
Well that looks a bit sparse for "775W" or "875W" but overall not as bad as I expected for a $15 power supply:
Primary:
Line filtering consists of 2 X-Caps, 4 Y-Caps, 2 coils, and 1 MOV, honestly not bad at this price point,
The bridge rectifier is a GBU806 8A 600V unit.
Primary caps are a pair of Changx 560uf 200V
Primary switchers are 2 4N50C MOSFETs rated at 4A 500V
Secondary:
2 MBR20100CT 20A 100V Schottky Rectifiers on the 12V Rail(s)
1 STPS2045CT 20A 45V Schottky Rectifiers on the 5V Rail
1 STPS2045CT 20A 45V Schottky Rectifiers on the 3.3V Rail
3 Changx GR 1000uf 16v caps on the 12v Rail(s)
2 Changx GR 1000uf 10v caps on the 5V rail
1 Changx GR 1000uf 10v cap on the 3.3V rail
1 Changx GR 470uf 16v cap on the 5vsb
The fan is a BOK BDM1202S 120mm sleeve bearing fan.
The soldering isn't too bad considering the price point:
Lets see how it does under a 257W load (12V@14A, 5V@10A, 3.3V@12A):
The 12V rail is at 12.221V:
The 5V rail is at 4.8925V:
The 3.3 V is at3.2239V:
Lets take a look at the ripple, the scale on the oscilloscope is set to 10mv per division.
The 12V rail has around 15-20ma ripple:
The 5V rail also around 20mv ripple:
Same story on the 3.3V rail around 15-20ma ripple:
Efficiency is around 81% with the PSU drawing 317W at the mains for a 257W load:
Honestly I was somewhat pleasantly surprised by this PSU, while it certainly isn't really a "775W" or "875W" unit as the manufacture claims (more like 350-400W at best) it isn't nearly as bad as I would have expected at this price point. Aside from rather questionable cap choices (Changx, and more capacitance would be nice) it isn't all that terrible for a "cheap" PSU (that being said the prices seem highly variable and it wouldn't be any kind of a "value" at a price above $25).
The Packaging is about as basic as you can get, a plain cardboard box with the PSU wrapped in bubble wrap and a power cable inside:
Looking at the PSU itself, this is a non-modular unit with a 120mm fan and basic black paint job:
The Label is even more ambitious than the product listing page, claiming 875W
:Lets take a look inside:
Well that looks a bit sparse for "775W" or "875W" but overall not as bad as I expected for a $15 power supply:
Primary:
Line filtering consists of 2 X-Caps, 4 Y-Caps, 2 coils, and 1 MOV, honestly not bad at this price point,
The bridge rectifier is a GBU806 8A 600V unit.
Primary caps are a pair of Changx 560uf 200V
Primary switchers are 2 4N50C MOSFETs rated at 4A 500V
Secondary:
2 MBR20100CT 20A 100V Schottky Rectifiers on the 12V Rail(s)
1 STPS2045CT 20A 45V Schottky Rectifiers on the 5V Rail
1 STPS2045CT 20A 45V Schottky Rectifiers on the 3.3V Rail
3 Changx GR 1000uf 16v caps on the 12v Rail(s)
2 Changx GR 1000uf 10v caps on the 5V rail
1 Changx GR 1000uf 10v cap on the 3.3V rail
1 Changx GR 470uf 16v cap on the 5vsb
The fan is a BOK BDM1202S 120mm sleeve bearing fan.
The soldering isn't too bad considering the price point:
Lets see how it does under a 257W load (12V@14A, 5V@10A, 3.3V@12A):
The 12V rail is at 12.221V:
The 5V rail is at 4.8925V:
The 3.3 V is at3.2239V:
Lets take a look at the ripple, the scale on the oscilloscope is set to 10mv per division.
The 12V rail has around 15-20ma ripple:
The 5V rail also around 20mv ripple:
Same story on the 3.3V rail around 15-20ma ripple:
Efficiency is around 81% with the PSU drawing 317W at the mains for a 257W load:
Honestly I was somewhat pleasantly surprised by this PSU, while it certainly isn't really a "775W" or "875W" unit as the manufacture claims (more like 350-400W at best) it isn't nearly as bad as I would have expected at this price point. Aside from rather questionable cap choices (Changx, and more capacitance would be nice) it isn't all that terrible for a "cheap" PSU (that being said the prices seem highly variable and it wouldn't be any kind of a "value" at a price above $25).
Attached Files
what a difference a cap change makes! cant hardly believe it! ah well... i guess this is solid proof good caps do make a difference. from 15 dollar junk psu to a va-va-voom psu that can compete with even high quality units from seasonic and superflower. with that recap, i'd bet the psu can do 350-400w without the ripple getting out of control.
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