The Games People Play

The Ugly Truth About Power Supply Specifications

It’s unfortunate, but true, that some manufacturers exaggerate or distort their product specifications to make their products appear to be better than they really are. Take, for example, the specification for power supplies in the PC market.

What does 200 Watts mean to you? It SHOULD mean that the power supply is capable of providing a regulated output of 200 Watts and delivering that power under ALL input conditions. However, some people have a different way of calculating the maximum output power of a power supply. I will give two examples of well-known power supplies and illustrate the difference in the way the output power has been calculated.

Vendor A, a well respected manufacturer of power supplies for the PC industry sells a 150 Watt PSU. Its specs are conservative and easily understood by most PC users. The Unit delivers the stated currents under all input voltage conditions (7v to 18v). The PSU easily delivers the 150Watts of specified output power and is well regulated (2% total regulation on critical outputs).

Vendor B, on the other hand, has a very different way of calculating output power. Vendor B claims 200 Watts of output power, but 162 Watts of this is UNREGULATED. What does this mean? It means that the input voltage (10.5 – 15 Volts) is fed DIRECTLY TO THE +12 VOLT OUTPUT PIN WITH NO REGULATION FROM THE PSU. In this case, the unregulated +12V output line represents 162Watts out of 200 Watts, or over 80% of the total claimed output power. If you calculate the ACTUAL power by multiplying the Max Load (amps) by the regulated voltages, the PSU is actually delivering only 61 Watts of TOTAL REGULATED POWER.

	Vendor A			Vendor B
Output Voltage	Max Load (Amps)	Power (Watts)	Regulation	Max Load (Amps)	Power (Watts)	Regulation
+5v (Amps)	10	50	2%	6	30	+/-5%
+5vsb (Amps)	1	5	2%	2	10	+/-5%
+3.3v (Amps)	10	33	2%	6	19.8	+/-5%
+12v (Amps)	5	60	2%	13.5	162	UNREGULATED
-12v (Amps)	0.2	2.4	10%	0.1	1.2	+/-10%
Total Claimed Output Power (Watts)		150.4			223
Minus Unregulated Power (Watts)		0			162
Total Regulated Output Power (Watts)		150.4			61

= 162 WATTS

UN-REGULATED

POWER

= 61 WATTS

REGULATED

POWER

= 200 WATTS ???

So what’s the harm in exaggerating the output power? Plenty! Many people would glance at the Total Power spec and automatically assume that Vendor B’s PSU was able to provide much more power to their PC system than Vendor A. When, in fact, it is merely a 60 Watt PSU and can only provide 40% of the regulated power of Vendor A’s unit.

Again, it’s unfortunate, but this seems to becoming a common practice in the PC marketplace where many people do not understand the “fine print”. We highly encourage you to DO YOUR HOMEWORK! Do not rely on a manufacturer’s claim of total output power. Look for the detailed specs on each of the output voltages and match this with your PC’s requirements. That’s the only way to avoid “The Games People Play”.