Burnselk - does the fan inside the PSU turn at all? I assume XL866 is 866 MHz, right? It's not under warranty, correct?
A standard drive connector should have 5 and 12 volts, positive and negative may be printed on one of your drives (I don't remember the pinout). Check one of the spare Molex plugs, or unplug the CD or DVD player / burner and use that one. As for checking 3.3 volts, sorry I can't help.
I lost a motherboard by using a cheap PS once. I installed a higher quality brand in my main PC, and haven't had a problem since. Two power supplies may both promise 350 watts for example, but the good one has more amps at each voltage and will give you the full 350 before it fails.
I hope you get your PC back up quickly.
And yes, do be careful around electricity.
you will get about 55-60 volts on each side so 55+55=110 volts or 60+60=120 volts. That is where you get your 110-120v home electricity.
I just tested my outlet with my Fluke 16 (I'm in Heating and Air Conditioning). Hot to neutral = 121.8V. Hot to ground = 121.8V. But neutral to ground, zero. (Neutral and ground should be wired together at the circuit breaker box, IIRC.)
When I checked the 240 volt outlet (electric dryer) I got 121.8, 121.9, and 243.7. This might have been what you were thinking of. One of my mates in HVAC night school, "Sparky", learned this the hard way. (And just for the record, I did not start that fire. That was another guy).
I believe "sb" is "standby". I think this is only important if you set the power saving features to wake up when the mouse is bumped, etc.
It may be impossible to find such a low-power (188 watts!!) power supply these days. And if you are using a CD/DVD burner (or you wish to add a SCSI chain), you will likely want to replace it with at least 250 watts.
(In fact, some high-powered "gamer" video cards suck so much power they require their own Molex connector right on the board!)