P611C is REV A00

YU822 is REV A00

CK520 is REV A01

U723D has an active north bridge cooling fan which the other three boards don’t have suggesting it is REV A01. "FEMALE" in description refers to ?

eBay seller sometimes lists XPS 710 or 700 under the name of 720.  Buyer aware​ 

look up exact model using service tag of pc and ask seller to disclose motherboard DP/N.  some 700/710 may have been upgraded to 720, so motherboard DP/N or rear IO panel pic are final proof of XPS 720.

The XPS 710 shipped with older Core 2 Duo and initial Core 2 Quad processors. The XPS 720 improved motherboard capability and BIOS support to officially handle faster 45nm/65nm quad-core processors like the Q6600, QX6850, and Q9450, with users successfully running even higher Yorkfield chips.

The main difference between the Dell XPS 700 and the XPS 710 is that the Dell XPS 710 introduced support for Intel's quad-core processors, whereas the Dell XPS 700 originally launched with dual-core Intel Core 2 Duo and Pentium Extreme Edition processors

Not easy to swap motherboard from 700/710 to 720 board in same case.  At least IO pinout are different.

Dell used to offer XPS 700 upgrade kit.

GT661 or CK520 XPS 720 Motherboard
KU128 H2C Liquid Cooling Device
XU567 Front Panel PWA Assembly Black
TM476 Front Panel Ribbon Cable
HN362 Front Panel Retention Device
16DYP Front Panel Retention Device Screws (x2)
GR709 Front Panel Audio Cable
WJ206 Replacement Front Panel Cosmetic Insert Black
XU556 Rear I/O Panel

if motherboard needs to be replaced it is better to use same pc model board (maybe not same DP/N)

front panel ribbon cable

if it is 28 pin: 720

if it is 40 pin: 700 or 710.

​ 

To upgrade 700/710 motherboard to 720 not only do user need to buy the 720 board but also front IO assembly for 720 (with 28 pin front panel I/O connector) and 28 pin front IO ribbon cable for 720.  

https://www.ebay.com/itm/361907070919

​Of note, front panel assembly with 40 pin front panel I/O connector are for 700/710.  not for 720.

700 rear IO panel is not compatible with 720 rear IO panel

here is a pro tip without service tag or motherboard DP/N to quickly tell from a glimpse of rear IO whether seller listed "XPS 720" is actually 700 or 710.

XPS 700/710 rear IO has a serial connector

XPS 720 rear IO has no serial connector

Since I prefer minimal engineering to preserve the unique 720/710/700 case appeal and do not plan to change from BTX to ATX (which involves cutting case rear panel), I see two requirements: having a working back up 720 motherboard and proprietary power supply with 24 and 20 pin connectors

oem psu 1-KW Power Supply 750-KW Power Supply 24 pin connector

DC Power Connector P1  

18-AWG Wire Color 
1 +3.3 VDC Orange +3.3 VDC Orange 
2 +3.3 VDC/SE Orange +3.3 VDC/SE Orange 
3 COM Black COM Black 
4 +5 VDC Red +5 VDC Red 
5 COM Black COM Black 
6 +5 VDC Red +5 VDC Red 
7 COM Black COM Black 
8 POK Gray POK Gray 
9 +5 VFP  Purple +5 VFP  Purple 
10 +12 VD DC/SE Yellow/White +12 VD DC/SE Yellow/White 
11 +12 VD DC Yellow/White +12 VD DC Yellow/White 
12 +3.3 VDC Orange +3.3 VDC Orange 
13 +3.3 VDC Orange +3.3 VDC Orange 
14 -12 VDC Blue -12 VDC Blue 
15 COM Black COM Black 
16 PS_ON Green PS_ON Green 
17 COM Black COM Black 
18 COM Black COM Black 
19 COM Black COM Black 
20 N/C N/A N/C N/A 
21 +5 VDC/SE Red +5 VDC/SE Red 
22 +5 VDC Red +5 VDC Red 
23 +5 VDC Red +5 VDC Red 
24 COM Black COM Black 

oem psu 20 pin connector

DC Power Connector P2  
  
18-AWG Wire Color 
1 +12 VC DC Blue/White +12 VC DC Blue/White 
2 +12 VC DC Blue/White +12 VC DC Blue/White 
3 COM Black COM Black 
4 COM Black COM Black 
5 +12 VA DC/SE Yellow +12 VA DC/SE Yellow 
6 +12 VA DC Yellow +12 VA DC Yellow 
7 COM Black COM Black 
8 COM Black COM Black 
9 +12 VB DC/SE White +12 VB DC/SE White 
10 +12 VB DC White +12 VB DC White 
11 +12 VC DC/SE Blue/White +12 VC DC/SE Blue/White 
12 COM Black COM Black 
13 COM Black COM Black 
14 COM Black COM Black 
15 +12 VA DC Yellow +12 VA DC Yellow 
16 COM Black COM Black 
17 COM Black COM Black 
18 COM Black COM Black 
19 +12 VB DC White +12 VB DC White 
20 NC N/A NC N/A 

compared oem 24 pin with ATX 24 pin, pin by pin, I confirm OEM 24 pin is standard ATX 24 pin

1 3.3V Orange+3.3 VDC
2 3.3V Orange+3.3 VDC
3 COM Black Ground
4 5V Red +5 VDC
5 COM Black Ground
6 5V Red +5 VDC
7 COM Black Ground
8 PWR_OK Gray (+5 VDC when power is Ok)
9 5VSB Purple +5 VDC Standby Voltage (max 10mA)
10 12V Yellow +12 VDC
11 12V Yellow +12 VDC
12 3.3V Orange+3.3 VDC
13 3.3V Orange+3.3 VDC
14-12V Blue-12 VDC
15 COM Black Ground
16 /PS_ON Green Short this pin to GND to switch on 
17 COM Black Ground
18 COM Black Ground
19 COM Black Ground
20-5V White-5 VDC  (optional)
21 +5V Red +5 VDC
22 +5V Red +5 VDC
23 +5V Red +5 VDC
24 COM Black Ground

oem 10 pin connector 

This can be sourced from 4 pin molex connectors

it needs 9 x 12V wires.

(bold=12V,  italic=Gnd, pin 20=n/c)

there are quite a few 710/700 front IO assembly on the market but virtually no 720 front IO.  to obtain a 720 front IO now one would need to find a nonworking 720 unit to salvage part.

pic of 700/710 front IO which has 40 pin cable FJ158

note the older IO board has a strange Dell plug WJ459. It doesn’t go to motherboard.

whereas the 720 IO has a white 10 pin audio connector with cable connected to motherboard audio socket too.  The 710/700 IO and motherboard does not have this white audio socket.

XPS 720/710/700 psu

750w (2 x PCIe 6 pin)

1000w (4 x PICe 6 pin)