Is this Motherboard ATX And does it work with ATX psus?

The ATX1 is probably referring to the ATX power connector. What make and model is your motherboard? If it is from a dell, HP or similar, it may be a proprietary form factor.

What hardware do you have in your computer? Can't confirm what PSU model will work without power requirements. Very good chance a standard ATX PSU will work though.
 
Which model and form factor of the inspiron? Some have one-off PSU shapes or odd mounting methods. I think any of the ones with a normal sized PSU have the correct mounting screw holes on the back panel.

The PSU's will work electronically with modern units such as Corsairs. Size is the concern now.