Optiplex 7010/9010/3010 MT.  These use standard 24/4 pin ATX psu. the next gen optiplex 7020/9020/3020/XE2 MT also use ATX form factor psu but proprietary 8/4 pin connectors.  But these cases support standard 24/4 pin psu too if users acquire 24 to 8 pin adapter or use non-Dell microATX mobo. Optiplex 3040/5040/7040 is the first gen Dell breaks ATX standard and begins to use proprietary TFX psu as well as odd shaped non standard mobo form factor.
What was the latest Dell mini tower line to come with a conventional ATX type power supply as opposed to the TFX type used now?
Last Dell Mini Tower to offer ATX power supply