Contents
Besta PT-550
In last year’s el-cheapo power supply roundup, the first PSU I tested was a Besta PT-500, and it was pretty average, to put it lightly. Now, I’m going to find out if the PT-500’s 550W big brother can do any better
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The only major difference between the PT-500 and PT-550 (other than the extra 6A on the 5V rail), is the 120mm fan. The PT-500 used a rear-mounted 80mm fan. The rust on the grilles suggests that this one probably came from some one who lived right on the coast.
Load Testing
Test 1 (118.26W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 4.85A | 12.13V | 25.2mV |
| 5V | 5.04A | 5.04V | 15.6mV |
| 3.3V | 10.15A | 3.35V | 52.4mV |
| −12V | 0A | −12.56V | 6.0mV |
| 5Vsb | 0A | 5.10V | 11.2mV |
| AC Power | 146.98W | ||
| Efficiency | 80.46% | ||
| Power Factor | 0.63 | ||
Test 2 (208.4W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 9.71A | 12.14V | 42.2mV |
| 5V | 10.02A | 5.01V | 20.2mV |
| 3.3V | 10.15A | 3.35V | 53.8mV |
| −12V | 0.1A | −12.42V | 30.2mV |
| 5Vsb | 1.0A | 5.0V | 13.0mV |
| AC Power | 253.07W | ||
| Efficiency | 82.35% | ||
| Power Factor | 0.65 | ||
Test 3 (264.48W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 14.42A | 12.02V | 49.8mV |
| 5V | 10.08A | 5.04V | 20.2mV |
| 3.3V | 10.15A | 3.35V | 54.4mV |
| −12V | 0.11A | −12.66V | 38.2mV |
| 5Vsb | 1A | 4.98V | 15.0mV |
| AC Power | 321.88 | ||
| Efficiency | 82.17% | ||
| Power Factor | 0.66 | ||
Test 4 (318.32W Load – Cold)
| Rail | Load | Voltage | Ripple |
| 12V | 19.04A | 11.90V | 63.0mV |
| 5V | 10.14A | 5.07V | 22.8mV |
| 3.3V | 10.15A | 3.35V | 52.8mV |
| −12V | 0.11A | −12.90V | 48.4mV |
| 5Vsb | 0.99A | 4.97V | 17.2mV |
| AC Power | 393.25W | ||
| Efficiency | 80.95% | ||
| Power Factor | 0.64 | ||
If anything, this PSU actually did worse than its little brother, as it had much higher ripple levels on the 3.3V rail, which was slightly above the maximum allowable 50mV the whole time. To be fair, though, less than 5mV over is unlikely to have much effect on the lifespan of your hardware, so you’d probably get away with it. But still, lower ripple levels would be preferred. The voltage regulation was fine. With the exception of the -12V, all of the rails stayed within 2% of their nominal values at all times. The efficiency peaked at just over 82%, which is the best I’ve seen in this roundup so far. I attempted to increase the load by about 50W for another test, but the power supply exploded after less than a minute.
| Rail | Test 3 (264.48W) | Test 4 (318.32W) |
| 12V |  |
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| 5V |  |
 |
| 3.3V |  |
 |
| −12V |  |
 |
| 5Vsb |  |
 |
A Look Inside
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The input filtering consists of an X capacitor, two common-mode chokes, and a Y capacitor. It really could use some more capacitors and an MOV. Other than the somewhat worse input filtering, the primary side is very similar to the PT-500, using 470uF primary caps, and the same “13007” marked switchers. The primary caps appear to be made by Chemi-Con, but on closer inspection are clearly fake. The snap-in KMG series is obsolete, and real 105°C Chemi-Cons have brown sleeves (with the exceptions of LZA, LXZ and LXY which are dark blue, older KZE which were green, and KZJ and some TMZ which were black with gold print). I have since identified the switchers as being JD Semiconductors 13007 transistors, which are rated at 9A.
The 12V rectifier is a Shindengen Electric SF20LC30 super fast recovery rectifier rated at 20A. Interestingly, the PT-500 used a pair of 12A parts, which means it had 24A capacity in total, so this unit actually has a weaker 12V rail than its little brother. In all other respects, though, the secondary side is very similar to the PT-500. The 5V rail uses an STPS3045CW 30A Schottky rectifier, which isn’t adequate for a rail which is supposed to be able to deliver 43A. I couldn’t identify the manufacturer of the 3.3V rectifier, but the part number (MBR2045CT) suggests that it’s rated for 20A. The output filtering capacitors are all branded BH, which aren’t exactly known for high quality parts.
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The fan is from the same unknown manufacturer as the PT-500. The power supply lacks a fan controller, so it runs at full speed constantly, but this fan is probably a low speed model, since it wasn’t very loud. The heat sinks aren’t as bad as the ones used on the Excel, but there’s ample room for bigger heat sinks.
Specifications and Conclusions
| Real Wattage | 320W |
| OEM | Unknown |
| PFC | None |
| Price | $30 |
| ATX Connector type | 20+4 pin |
| Worst-case voltage regulation (12v, 5v, 3.3v) | 1.2%, 1.4%, 1.5% |
| Worst-case ripple (12v, 5v, 3.3v) | 63mV, 22.8mV, 54.4mV |
| Worst-case efficiency | 80.46% |
| Input filtering | Inadequate |
| CPU Connector | ATX12v (4 pin) |
| PCIe Connectors | None |
| Molex (Peripheral) Connectors | 4 |
| FDD Power connectors | 1 |
| SATA Power connectors | 1 |
Pros: Good voltage regulation
Cons: Can’t deliver labelled rating, Not enough connectors, Average ripple suppression, Low quality capacitors and fan, Inadequate input filtering.
Score: 3/10
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