using a pc powersupply to feed led strips

Yessir.
In addition to the 12V, 5V, and 3.3V I mentioned prior, those power supplies also provide a -12V rail.
Some power supplies will also provide a -5V rail as well, but I seem to recall them being phased out... so they would be on older supplies only.

Remaining wires include an Active Low Power Supply ON input, and 5V Standby supply, and a status output wire. (I can't recall the behaviour of this wire)

More often then not, they should have a sticker on the side broken up into logical groups that show the absolute maximum current output for any given rail (usually excluding standby, and status output.)
Sometimes they are grouped though, and will provide an absolute 'power' for 2 or more rails at a time. So drawing the limit of the 5V and 12V rail may still push the total power handling capability of the PSU higher than designed.

I have a number of these strewn through the house... They are cheap and apparently abundant.
I've used one to power a car audio head-unit and amp, even used one to power one of those 'road-side' air compressors to inflate some balloons xD

 

Only when I loaded the 3.3V (10ohms), it started to work well for the other voltages 12 and 5...

it was impossible to make it work by loading 5v or 12v (even with 1 or 2 ohm resistors).

 

Good job figuring that out.
It's not something I have ever seen required to be honest.