Bestec ATX-300-12Z Review

First Look

Bestec PSUs are famous for all the wrong reasons and are often referred to as “Worstec” for the PSUs they supplied for eMachines, which had problems with their transistor based 5vsb circuits which would cause the voltage to go way over 5v after a few years of use and cook the motherboard, but that problem only affects the 12E models. Since this is a 12Z, this unit is expected to be better.

_

This unit was removed from a newish HP Computer. HP really should know better than to use an outdated 5v heavy PSU in a new PC.

Load Testing

Test 1 (111W Load – Cold)

Rail	Load	Voltage
12V	4.67A	11.67V
5V	4.93A	4.93V
3.3V	9.94A	3.28V
−12V	0A	−12.48V
5Vsb	0A	4.91V

 

Test 2 (191W Load – Cold)

Rail	Load	Voltage
12V	9.28A	11.60V
5V	9.66A	4.83V
3.3V	9.7A	3.20V
−12V	0.1A	−12.46V
5Vsb	0.96A	4.81V

 

Test 3 (240W Load – Cold)

Rail	Load	Voltage
12V	9.46	11.82V
5V	19.08A	4.77V
3.3V	9.67A	3.19V
−12V	0.11A	−12.77V
5Vsb	0.96A	4.81V

 

Test 4 (303W Load – Hot)

Rail	Load	Voltage	Ripple
12V	11.88A	11.88V	43.1mV
5V	19.12A	4.78V	20mV
3.3V	19.7A	3.25V	10mV
−12V	0.11A	−12.76V	35.6mV
5Vsb	0.97A	4.87V	24.4mV

 

Test 5 (405W Load – Hot)

Rail	Load	Voltage	Ripple
12V	14.5A	12.08V	95mV
5V	28.26A	4.71V	41.2mV
3.3V	28.64A	3.15V	11.2mV
−12V	0.11A	−13.45V	76.9mV
5Vsb	0.97A	4.83V	25mV

 

The unit performed very well up to it’s labelled rating of 300W, since everything stayed within tolerances and the unit remained fairly quiet throughout. The ripple suppression was another plus. Once again, nothing went out of spec. For test 5, the unit was overloaded to 405W (136% of it’s rating). There, the −12v rail was at −13.45v, which is below the minimum −13.2v allowed in ATX specifications. The ripple, although significantly higher on some rails, was still in spec. After about 5 minutes, the Bestec went bang and died, although interestingly, there were no visible sparks or smoke. While the unit could do it’s labelled rating, we would have preferred it to shut down rather than fail when overloaded.

Rail	Test 4 (303W)	Test 5 (405W)
12V
5V
3.3V
−12V
5Vsb

A look inside

_

It seems like a shame this unit failed, since it is quite well built. Starting at the input filter, we have three X-caps, two common-mode chokes and three Y-caps (including the one after the rectifier), which is easily enough. On the primary, we have a 6A bridge rectifier, which will handle up to 528W from a 110v input or 1,104W from a 230v input (after de-rating to account for the non-linear load), which is more than enough for a 300W. The input capacitors are both 680μF parts made by CapXon which are more than enough for a 300W PSU. The presence of passive PFC is also nice to see for a low end unit. It uses a single-transistor forward design with a now rather charred ST Microelectronics STW9NK90Z MOSFET as the switching transistor, rated for up to 8A at 25°C and 5A at 100°C. It was clearly enough for the unit to manage 300W, but only just. The fact that there is only one transistor bolted to the primary heat sink shows that this unit doesn’t have the transistor based 5vsb circuit, so it isn’t prone to over-volting and frying the motherboard.

Moving on to the secondary, the silicon there is a bit more overspec’ed which is good, since it means that the primary switching transistor will fail first, which rarely kills any attached hardware. On the 12v rail, there are two 20A Schottky rectifiers which will allow for over double the labelled 19A. On the 5v, there are two 30A Schottkys, so the 5v rail should be capable of up to 60A. Double the labelled rating. On the 3.3v rail, there is a single 30A Schottky, which is just enough for the labelled 28A. All of the secondary capacitors are Jamicon brand, which is a major let down, since they aren’t much better than Fuhjyyu.

_

The fan on this unit is also a Jamicon. Thankfully, Jamicon are much better at making fans than they are at making capacitors.

Specifications

Real Wattage	300W
OEM	Bestec
PFC	Passive
Price	OEM – Not sold separately
ATX Connector	24 Pin only
CPU Connector	ATX12V (4 Pin)
PCI-E Connectors	None
Molex (Peripheral) Connectors	5
SATA Power Connectors	2
FDD Connectors	1

 

Conclusions

Pros: Can deliver its labelled rating, Quiet, No “Worstec killer 5vsb” circuit, Input filtering, Voltage regulation, Ripple suppression, PFC

Cons: Jamicon Capacitors, 24 pin only ATX Connector, no OPP

Bottom Line: It performed OK during the tests, but due to the fact that it exploded at 400W, you’d be better off with the Hipro HP-D3057F3H.

Score: 6.5/10

Discuss this review in our forum here!

Review sample source: Removed from PC