i've read the pdf docs, so if i choose to upgrade xfx radeon hd6670 with 1gb, no need to buy PSU with higher watts ?

The 990 MT has 265W power supply.  Never had issue with Older Optiplex 7XX models that had 305W power supply.  I do not recommend installing a 6670 with the stock 265W power supply.

http://www.dell.com/downloads/global/products/optix/en/optiplex-990-customer-brochure.pdf

The 6670 in the docs is a DELL OEM 6670 that has no fan and DDR3 ram slow clocked to not use TOO MUCH power.

Okey, DELL OEM 6670 is out of sale list, so it seems i can't get it now.

is Upgrading PSU okey ? i'm now considering corsair rm650.

OEM AMD has rebranded the HD 6670 to HD 7670

MUST BE EPS12v Certified.  The RM650 Conforms to ATX12V v2.4 and EPS 2.92 standards so its fine.

http://www.corsair.com/en/rm-series-rm650-80-plus-gold-certified-power-supply

 The following 430w, 450w  and 500w power supplies are compatible

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438015

http://www.newegg.com/Product/Product.aspx?Item=N82E16817182066

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438016

oh very important info.

1. i searched through dell.com by optiplex 990, there are many cards for upgrade such as NVIDIA® NVS™ 510 business graphics. NVS 510 compatible with 990MT without PSU change ?

2. if i go for upgrading my PSU by RM650 or EVGA 100-W1-500 so am i able to freely go for broad range of advanced graphics under the power limitation ?

K620 will work fine with stock Tower Power Supply.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814133560

 http://www.nvidia.com/object/product-quadro-600-us.html

I see where people have upgraded the PS - But I do not understand how they fit as the upgraded ones seem to have the fan on top. Not on the same side as the power plug.

Thank you so much.

I'm now considering nvidia quadro k620 or amd firepro w2100 maybe w4100.

"amd firepro w4100 has gddr5 memory but uses 51W power, is it ok ?"

---

newegg (also sapphire) spec says amd firepro w4100 needs min 500W PS and even lowest of class w2100 (which uses only 26W) needs min 400W BUT Nvidia and PNY not mentioning any min PS requirements for their Quadro 620card.

It seems confusing :(

Hi, Rockstar!

I have a Dell Optiplex 990 minitower.

I feel that it lacks power supply and am considering upgrading it.

All of three power supplies you mentioned above will be compatible with my Optiplex 990 mini-tower?

Thanks a lot for your valuable information!

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438016

Dell just listed AMD Radeon™ R5 240 for Optiplex 990MTs here:

http://accessories.dell.com/sna/productdetail.aspx?c=us&l=en&s=dhs&cs=19&sku=490-BCEP&mfgpid=208477

how this card will perform compared to HD5450 or HD6670 ?

R5 240 = $90 Card is not as good as the 6670 = $70 Card but  Better than the 5450= $40 card.

GDDR3 is slower and cheaper.  Minimum you want is GDDR5 Radeon 7750 aka R7 250.

The 5450 has

ROPs    4
Stream processors    80
Texture units   8

The 6670 has

ROPs    8
Stream processors    480
Texture units    24

The R7 250E  is the Radeon HD7750

That card is better and the recommended 75W max card.

ASUS R7250-1GD5 Radeon R7 250 1GB 128-Bit GDDR5

http://www.newegg.com/Product/Product.aspx?Item=N82E16814121800

Minimum you want is GDDR5 Radeon 7750 aka R7 250.

I replaced a 6670 with an R7 240 GDDR5, and not only did I get a boost in the Windows Experience Index, fan noise was sharply reduced.

Sapphire 11216-01-20G Radeon R7 240 1GB GDDR5 has 320 stream processors.

AVOID GDDR3 versions.

http://www.directron.com/112160120g.html