Inspiron 3020 desktop vs Inspiron 3020 small desktop

3020 desktop (minitower) is essentially the same 3910 with motherboard bios updated to support 13th gen cpu, whereas 3910 bios probably for 12th gen only.  Both have B660 chipset.  Chassis is identical.

The psu can both be upgraded to Dell 500w proprietary psu. Both mobo have Dell 8+4 pin.

the 500w psu has 8+4+4 white pin.  Leave one 4 pin unused.

user verified solution and positive evidence: Dell 500w power supply option compatible with the Inspiron 3910 and 3020 desktop. Part number: TPX56

D500EPS-01

7.28 x 4.72 x 2.44 inches

dimensions and connectors pic

On the other hand the Inspiron 3020 small desktop (SFF) has a different motherboard: 8+4+4 pin.  Chipset still B660.

being SFF means it can support low profile low power gpu only.

psu upgrade also limited as the 500w psu width (4.72 in) exceeds chassis width 3.65 in. (92.6 mm).  Stock psu is 180w only.  However user can still upgrade to Dell Optiplex 7000 SFF psu:

240W internal power supply unit (PSU), 85% Efficient, 80 Plus Bronze
260W internal power supply unit (PSU), 85% Efficient, 80 Plus Bronze
300W internal power supply unit (PSU), 92% Efficient, 80 Plus Platinum

H300EPS-01 L300EPS-01 AC300EPS-01 D300EPS-00

‎7.36 x 3.23 x 2.44 inches

184 x 82 x 62 mm.

The optiplex 7000 SFF has the same chassis width as Inspiron 3020 small desktop (SFF too).