Coputer to Lab power supply conversion

Hey everybody. I am a hobbyist in the field of electronics with no formal training. I have a pretty good understanding of components but know basically nothing about systems as a whole. I got my hands on an old computer supply and read about converting them for use as a lab power supply. The directions said the poower supply needs to be loaded to run, For their 450 watt power supply a 10 ohm 10 watt resistor was used. My power supply is only a 90 watt, 10 ohms sounds like overkill. I have a 250 ohm power resistor laying around. by my calculations this will pull about 45 milliamps at 12 volts. Does this sound like enough to load my 90 watt power supply? if not how many amps will it take? thanks in advance!