When looking for PSUs, look for enough wattage. Make sure it isn't just peak wattage you're looking at. Also, look for good amperage on the 3.3V, 5V and 12V rails.
You can use a 20+4 pin connector in 24-pin mobos.
PC P&C (PC power&cooling) = the best out there.
Voltage does match, assuming you're using the right PSU for the form factor. ie: ATX PSU with ATX mobo, AT with AT, etc.